Create collections on DfaNode as needed (#779)

src/Microsoft.AspNetCore.Routing/Internal/DfaGraphWriter.cs

@@ -64,9 +64,12 @@ namespace Microsoft.AspNetCore.Routing.Internal
                 // We can safely index into visited because this is a post-order traversal,
                 // all of the children of this node are already in the dictionary.
 
-                foreach (var literal in node.Literals)
+                if (node.Literals != null)
                 {
-                    writer.WriteLine($"{label} -> {visited[literal.Value]} [label=\"/{literal.Key}\"]");
+                    foreach (var literal in node.Literals)
+                    {
+                        writer.WriteLine($"{label} -> {visited[literal.Value]} [label=\"/{literal.Key}\"]");
+                    }
                 }
 
                 if (node.Parameters != null)
@@ -79,9 +82,12 @@ namespace Microsoft.AspNetCore.Routing.Internal
                     writer.WriteLine($"{label} -> {visited[node.CatchAll]} [label=\"/**\"]");
                 }
 
-                foreach (var policy in node.PolicyEdges)
+                if (node.PolicyEdges != null)
                 {
-                    writer.WriteLine($"{label} -> {visited[policy.Value]} [label=\"{policy.Key}\"]");
+                    foreach (var policy in node.PolicyEdges)
+                    {
+                        writer.WriteLine($"{label} -> {visited[policy.Value]} [label=\"{policy.Key}\"]");
+                    }
                 }
 
                 writer.WriteLine($"{label} [label=\"{node.Label}\"]");

src/Microsoft.AspNetCore.Routing/Matching/DfaMatcherBuilder.cs

@@ -105,7 +105,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
                         for (var j = 0; j < parents.Count; j++)
                         {
                             var parent = parents[j];
-                            parent.Matches.Add(endpoint);
+                            parent.AddMatch(endpoint);
                         }
                     }
 
@@ -139,15 +139,17 @@ namespace Microsoft.AspNetCore.Routing.Matching
                         var part = segment.Parts[0];
                         if (segment.IsSimple && part is RoutePatternLiteralPart literalPart)
                         {
+                            DfaNode next = null;
                             var literal = literalPart.Content;
-                            if (!parent.Literals.TryGetValue(literal, out var next))
+                            if (parent.Literals == null ||
+                                !parent.Literals.TryGetValue(literal, out next))
                             {
                                 next = new DfaNode()
                                 {
                                     PathDepth = parent.PathDepth + 1,
                                     Label = parent.Label + literal + "/",
                                 };
-                                parent.Literals.Add(literal, next);
+                                parent.AddLiteral(literal, next);
                             }
 
                             nextParents.Add(next);
@@ -157,7 +159,10 @@ namespace Microsoft.AspNetCore.Routing.Matching
                             // A catch all should traverse all literal nodes as well as parameter nodes
                             // we don't need to create the parameter node here because of ordering
                             // all catchalls will be processed after all parameters.
-                            nextParents.AddRange(parent.Literals.Values);
+                            if (parent.Literals != null)
+                            {
+                                nextParents.AddRange(parent.Literals.Values);
+                            }
                             if (parent.Parameters != null)
                             {
                                 nextParents.Add(parent.Parameters);
@@ -181,7 +186,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
                                 parent.CatchAll.CatchAll = parent.CatchAll;
                             }
 
-                            parent.CatchAll.Matches.Add(endpoint);
+                            parent.CatchAll.AddMatch(endpoint);
                         }
                         else if (segment.IsSimple && part.IsParameter)
                         {
@@ -195,7 +200,10 @@ namespace Microsoft.AspNetCore.Routing.Matching
                             }
 
                             // A parameter should traverse all literal nodes as well as the parameter node
-                            nextParents.AddRange(parent.Literals.Values);
+                            if (parent.Literals != null)
+                            {
+                                nextParents.AddRange(parent.Literals.Values);
+                            }
                             nextParents.Add(parent.Parameters);
                         }
                         else
@@ -213,7 +221,10 @@ namespace Microsoft.AspNetCore.Routing.Matching
                                 };
                             }
 
-                            nextParents.AddRange(parent.Literals.Values);
+                            if (parent.Literals != null)
+                            {
+                                nextParents.AddRange(parent.Literals.Values);
+                            }
                             nextParents.Add(parent.Parameters);
                         }
                     }
@@ -311,7 +322,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             List<DfaState> states,
             List<(JumpTableBuilder pathBuilder, PolicyJumpTableBuilder policyBuilder)> tableBuilders)
         {
-            node.Matches.Sort(_comparer);
+            node.Matches?.Sort(_comparer);
 
             var stateIndex = states.Count;
 
@@ -321,15 +332,18 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var pathBuilder = new JumpTableBuilder();
             tableBuilders.Add((pathBuilder, null));
 
-            foreach (var kvp in node.Literals)
+            if (node.Literals != null)
             {
-                if (kvp.Key == null)
+                foreach (var kvp in node.Literals)
                 {
-                    continue;
+                    if (kvp.Key == null)
-                }
+                    {
+                        continue;
+                    }
 
-                var transition = Transition(kvp.Value);
+                    var transition = Transition(kvp.Value);
-                pathBuilder.AddEntry(kvp.Key, transition);
+                    pathBuilder.AddEntry(kvp.Key, transition);
+                }
             }
 
             if (node.Parameters != null &&
@@ -360,7 +374,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
                 pathBuilder.ExitDestination = pathBuilder.DefaultDestination;
             }
 
-            if (node.PolicyEdges.Count > 0)
+            if (node.PolicyEdges != null && node.PolicyEdges.Count > 0)
             {
                 var policyBuilder = new PolicyJumpTableBuilder(node.NodeBuilder);
                 tableBuilders[stateIndex] = (pathBuilder, policyBuilder);
@@ -384,7 +398,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
         // endpoint.
         internal Candidate[] CreateCandidates(IReadOnlyList<Endpoint> endpoints)
         {
-            if (endpoints.Count == 0)
+            if (endpoints == null || endpoints.Count == 0)
             {
                 return Array.Empty<Candidate>();
             }
@@ -502,7 +516,8 @@ namespace Microsoft.AspNetCore.Routing.Matching
 
         private int[] GetGroupLengths(DfaNode node)
         {
-            if (node.Matches.Count == 0)
+            var nodeMatches = node.Matches;
+            if (nodeMatches == null || nodeMatches.Count == 0)
             {
                 return Array.Empty<int>();
             }
@@ -510,16 +525,16 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var groups = new List<int>();
 
             var length = 1;
-            var exemplar = node.Matches[0];
+            var exemplar = nodeMatches[0];
 
-            for (var i = 1; i < node.Matches.Count; i++)
+            for (var i = 1; i < nodeMatches.Count; i++)
             {
-                if (!_comparer.Equals(exemplar, node.Matches[i]))
+                if (!_comparer.Equals(exemplar, nodeMatches[i]))
                 {
                     groups.Add(length);
                     length = 0;
 
-                    exemplar = node.Matches[i];
+                    exemplar = nodeMatches[i];
                 }
 
                 length++;
@@ -561,7 +576,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
 
         private void ApplyPolicies(DfaNode node)
         {
-            if (node.Matches.Count == 0)
+            if (node.Matches == null || node.Matches.Count == 0)
             {
                 return;
             }
@@ -578,7 +593,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
                 for (var j = 0; j < work.Count; j++)
                 {
                     var parent = work[j];
-                    if (!nodeBuilder.AppliesToNode(parent.Matches))
+                    if (!nodeBuilder.AppliesToNode(parent.Matches ?? (IReadOnlyList<Endpoint>)Array.Empty<Endpoint>()))
                     {
                         // This node-builder doesn't care about this node, so add it to the list
                         // to be processed by the next node-builder.
@@ -588,7 +603,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
 
                     // This node-builder does apply to this node, so we need to create new nodes for each edge,
                     // and then attach them to the parent.
-                    var edges = nodeBuilder.GetEdges(parent.Matches);
+                    var edges = nodeBuilder.GetEdges(parent.Matches ?? (IReadOnlyList<Endpoint>)Array.Empty<Endpoint>());
                     for (var k = 0; k < edges.Count; k++)
                     {
                         var edge = edges[k];
@@ -598,17 +613,20 @@ namespace Microsoft.AspNetCore.Routing.Matching
                             Label = parent.Label + " " + edge.State.ToString(),
                         };
 
-                        next.Matches.AddRange(edge.Endpoints);
+                        if (edge.Endpoints.Count > 0)
+                        {
+                            next.AddMatches(edge.Endpoints);
+                        }
                         nextWork.Add(next);
 
-                        parent.PolicyEdges.Add(edge.State, next);
+                        parent.AddPolicyEdge(edge.State, next);
                     }
 
                     // Associate the node-builder so we can build a jump table later.
                     parent.NodeBuilder = nodeBuilder;
 
                     // The parent no longer has matches, it's not considered a terminal node.
-                    parent.Matches.Clear();
+                    parent.Matches?.Clear();
                 }
 
                 work = nextWork;

src/Microsoft.AspNetCore.Routing/Matching/DfaNode.cs

@@ -14,13 +14,6 @@ namespace Microsoft.AspNetCore.Routing.Matching
     [DebuggerDisplay("{DebuggerToString(),nq}")]
     internal class DfaNode
     {
-        public DfaNode()
-        {
-            Literals = new Dictionary<string, DfaNode>(StringComparer.OrdinalIgnoreCase);
-            Matches = new List<Endpoint>();
-            PolicyEdges = new Dictionary<object, DfaNode>();
-        }
-
         // The depth of the node. The depth indicates the number of segments
         // that must be processed to arrive at this node.
         //
@@ -30,9 +23,9 @@ namespace Microsoft.AspNetCore.Routing.Matching
         // Just for diagnostics and debugging
         public string Label { get; set; }
         
-        public List<Endpoint> Matches { get; }
+        public List<Endpoint> Matches { get; private set; }
 
-        public Dictionary<string, DfaNode> Literals { get; }
+        public Dictionary<string, DfaNode> Literals { get; private set; }
 
         public DfaNode Parameters { get; set; }
 
@@ -40,13 +33,58 @@ namespace Microsoft.AspNetCore.Routing.Matching
 
         public INodeBuilderPolicy NodeBuilder { get; set; }
 
-        public Dictionary<object, DfaNode> PolicyEdges { get; }
+        public Dictionary<object, DfaNode> PolicyEdges { get; private set; }
+
+        public void AddPolicyEdge(object state, DfaNode node)
+        {
+            if (PolicyEdges == null)
+            {
+                PolicyEdges = new Dictionary<object, DfaNode>();
+            }
+
+            PolicyEdges.Add(state, node);
+        }
+
+        public void AddLiteral(string literal, DfaNode node)
+        {
+            if (Literals == null)
+            {
+                Literals = new Dictionary<string, DfaNode>(StringComparer.OrdinalIgnoreCase);
+            }
+
+            Literals.Add(literal, node);
+        }
+
+        public void AddMatch(Endpoint endpoint)
+        {
+            if (Matches == null)
+            {
+                Matches = new List<Endpoint>();
+            }
+
+            Matches.Add(endpoint);
+        }
+
+        public void AddMatches(IEnumerable<Endpoint> endpoints)
+        {
+            if (Matches == null)
+            {
+                Matches = new List<Endpoint>(endpoints);
+            }
+            else
+            {
+                Matches.AddRange(endpoints);
+            }
+        }
 
         public void Visit(Action<DfaNode> visitor)
         {
-            foreach (var kvp in Literals)
+            if (Literals != null)
             {
-                kvp.Value.Visit(visitor);
+                foreach (var kvp in Literals)
+                {
+                    kvp.Value.Visit(visitor);
+                }
             }
 
             // Break cycles
@@ -61,9 +99,12 @@ namespace Microsoft.AspNetCore.Routing.Matching
                 CatchAll.Visit(visitor);
             }
 
-            foreach (var kvp in PolicyEdges)
+            if (PolicyEdges != null)
             {
-                kvp.Value.Visit(visitor);
+                foreach (var kvp in PolicyEdges)
+                {
+                    kvp.Value.Visit(visitor);
+                }
             }
 
             visitor(this);
@@ -76,9 +117,12 @@ namespace Microsoft.AspNetCore.Routing.Matching
             builder.Append(" d:");
             builder.Append(PathDepth);
             builder.Append(" m:");
-            builder.Append(Matches.Count);
+            builder.Append(Matches?.Count ?? 0);
             builder.Append(" c: ");
-            builder.Append(string.Join(", ", Literals.Select(kvp => $"{kvp.Key}->({FormatNode(kvp.Value)})")));
+            if (Literals != null)
+            {
+                builder.Append(string.Join(", ", Literals.Select(kvp => $"{kvp.Key}->({FormatNode(kvp.Value)})")));
+            }
             return builder.ToString();
             
             // DfaNodes can be self-referential, don't traverse cycles.

test/Microsoft.AspNetCore.Routing.Tests/Matching/DfaMatcherBuilderTest.cs

@@ -30,7 +30,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             // Assert
             Assert.Same(endpoint, Assert.Single(root.Matches));
             Assert.Null(root.Parameters);
-            Assert.Empty(root.Literals);
+            Assert.Null(root.Literals);
         }
 
         [Fact]
@@ -46,21 +46,21 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
             Assert.Null(root.Parameters);
 
             var next = Assert.Single(root.Literals);
             Assert.Equal("a", next.Key);
 
             var a = next.Value;
-            Assert.Empty(a.Matches);
+            Assert.Null(a.Matches);
             Assert.Null(a.Parameters);
 
             next = Assert.Single(a.Literals);
             Assert.Equal("b", next.Key);
 
             var b = next.Value;
-            Assert.Empty(b.Matches);
+            Assert.Null(b.Matches);
             Assert.Null(b.Parameters);
 
             next = Assert.Single(b.Literals);
@@ -69,7 +69,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var c = next.Value;
             Assert.Same(endpoint, Assert.Single(c.Matches));
             Assert.Null(c.Parameters);
-            Assert.Empty(c.Literals);
+            Assert.Null(c.Literals);
         }
 
         [Fact]
@@ -85,21 +85,21 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
-            Assert.Empty(root.Literals);
+            Assert.Null(root.Literals);
 
             var a = root.Parameters;
-            Assert.Empty(a.Matches);
+            Assert.Null(a.Matches);
-            Assert.Empty(a.Literals);
+            Assert.Null(a.Literals);
 
             var b = a.Parameters;
-            Assert.Empty(b.Matches);
+            Assert.Null(b.Matches);
-            Assert.Empty(b.Literals);
+            Assert.Null(b.Literals);
 
             var c = b.Parameters;
             Assert.Same(endpoint, Assert.Single(c.Matches));
             Assert.Null(c.Parameters);
-            Assert.Empty(c.Literals);
+            Assert.Null(c.Literals);
         }
 
         [Fact]
@@ -115,21 +115,21 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
-            Assert.Empty(root.Literals);
+            Assert.Null(root.Literals);
 
             var a = root.Parameters;
 
             // The catch all can match a path like '/a'
             Assert.Same(endpoint, Assert.Single(a.Matches));
-            Assert.Empty(a.Literals);
+            Assert.Null(a.Literals);
             Assert.Null(a.Parameters);
 
             // Catch-all nodes include an extra transition that loops to process
             // extra segments.
             var catchAll = a.CatchAll;
             Assert.Same(endpoint, Assert.Single(catchAll.Matches));
-            Assert.Empty(catchAll.Literals);
+            Assert.Null(catchAll.Literals);
             Assert.Same(catchAll, catchAll.Parameters);
             Assert.Same(catchAll, catchAll.CatchAll);
         }
@@ -148,13 +148,13 @@ namespace Microsoft.AspNetCore.Routing.Matching
 
             // Assert
             Assert.Same(endpoint, Assert.Single(root.Matches));
-            Assert.Empty(root.Literals);
+            Assert.Null(root.Literals);
 
             // Catch-all nodes include an extra transition that loops to process
             // extra segments.
             var catchAll = root.CatchAll;
             Assert.Same(endpoint, Assert.Single(catchAll.Matches));
-            Assert.Empty(catchAll.Literals);
+            Assert.Null(catchAll.Literals);
             Assert.Same(catchAll, catchAll.Parameters);
         }
 
@@ -174,19 +174,19 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
             Assert.Null(root.Parameters);
 
             var next = Assert.Single(root.Literals);
             Assert.Equal("a", next.Key);
 
             var a = next.Value;
-            Assert.Empty(a.Matches);
+            Assert.Null(a.Matches);
 
             Assert.Equal(2, a.Literals.Count);
 
             var b1 = a.Literals["b1"];
-            Assert.Empty(b1.Matches);
+            Assert.Null(b1.Matches);
             Assert.Null(b1.Parameters);
 
             next = Assert.Single(b1.Literals);
@@ -195,10 +195,10 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var c1 = next.Value;
             Assert.Same(endpoint1, Assert.Single(c1.Matches));
             Assert.Null(c1.Parameters);
-            Assert.Empty(c1.Literals);
+            Assert.Null(c1.Literals);
 
             var b2 = a.Literals["b2"];
-            Assert.Empty(b2.Matches);
+            Assert.Null(b2.Matches);
             Assert.Null(b2.Parameters);
 
             next = Assert.Single(b2.Literals);
@@ -207,7 +207,59 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var c2 = next.Value;
             Assert.Same(endpoint2, Assert.Single(c2.Matches));
             Assert.Null(c2.Parameters);
-            Assert.Empty(c2.Literals);
+            Assert.Null(c2.Literals);
+        }
+
+        [Fact]
+        public void BuildDfaTree_MultipleEndpoint_LiteralDifferentCase()
+        {
+            // Arrange
+            var builder = CreateDfaMatcherBuilder();
+
+            var endpoint1 = CreateEndpoint("a/b1/c");
+            builder.AddEndpoint(endpoint1);
+
+            var endpoint2 = CreateEndpoint("A/b2/c");
+            builder.AddEndpoint(endpoint2);
+
+            // Act
+            var root = builder.BuildDfaTree();
+
+            // Assert
+            Assert.Null(root.Matches);
+            Assert.Null(root.Parameters);
+
+            var next = Assert.Single(root.Literals);
+            Assert.Equal("a", next.Key);
+
+            var a = next.Value;
+            Assert.Null(a.Matches);
+
+            Assert.Equal(2, a.Literals.Count);
+
+            var b1 = a.Literals["b1"];
+            Assert.Null(b1.Matches);
+            Assert.Null(b1.Parameters);
+
+            next = Assert.Single(b1.Literals);
+            Assert.Equal("c", next.Key);
+
+            var c1 = next.Value;
+            Assert.Same(endpoint1, Assert.Single(c1.Matches));
+            Assert.Null(c1.Parameters);
+            Assert.Null(c1.Literals);
+
+            var b2 = a.Literals["b2"];
+            Assert.Null(b2.Matches);
+            Assert.Null(b2.Parameters);
+
+            next = Assert.Single(b2.Literals);
+            Assert.Equal("c", next.Key);
+
+            var c2 = next.Value;
+            Assert.Same(endpoint2, Assert.Single(c2.Matches));
+            Assert.Null(c2.Parameters);
+            Assert.Null(c2.Literals);
         }
 
         [Fact]
@@ -226,20 +278,20 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
             Assert.Null(root.Parameters);
 
             var next = Assert.Single(root.Literals);
             Assert.Equal("a", next.Key);
 
             var a = next.Value;
-            Assert.Empty(a.Matches);
+            Assert.Null(a.Matches);
 
             next = Assert.Single(a.Literals);
             Assert.Equal("b", next.Key);
 
             var b = next.Value;
-            Assert.Empty(b.Matches);
+            Assert.Null(b.Matches);
             Assert.Null(b.Parameters);
 
             next = Assert.Single(b.Literals);
@@ -251,10 +303,10 @@ namespace Microsoft.AspNetCore.Routing.Matching
                 e => Assert.Same(endpoint1, e),
                 e => Assert.Same(endpoint2, e));
             Assert.Null(c1.Parameters);
-            Assert.Empty(c1.Literals);
+            Assert.Null(c1.Literals);
 
             var b2 = a.Parameters;
-            Assert.Empty(b2.Matches);
+            Assert.Null(b2.Matches);
             Assert.Null(b2.Parameters);
 
             next = Assert.Single(b2.Literals);
@@ -263,7 +315,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var c2 = next.Value;
             Assert.Same(endpoint2, Assert.Single(c2.Matches));
             Assert.Null(c2.Parameters);
-            Assert.Empty(c2.Literals);
+            Assert.Null(c2.Literals);
         }
 
         [Fact]
@@ -282,18 +334,18 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
             Assert.Null(root.Parameters);
 
             var next = Assert.Single(root.Literals);
             Assert.Equal("a", next.Key);
 
             var a = next.Value;
-            Assert.Empty(a.Matches);
+            Assert.Null(a.Matches);
-            Assert.Empty(a.Literals);
+            Assert.Null(a.Literals);
 
             var b = a.Parameters;
-            Assert.Empty(b.Matches);
+            Assert.Null(b.Matches);
             Assert.Null(b.Parameters);
 
             next = Assert.Single(b.Literals);
@@ -305,7 +357,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
                 e => Assert.Same(endpoint1, e),
                 e => Assert.Same(endpoint2, e));
             Assert.Null(c.Parameters);
-            Assert.Empty(c.Literals);
+            Assert.Null(c.Literals);
         }
 
         [Fact]
@@ -324,7 +376,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
             Assert.Null(root.Parameters);
 
             var next = Assert.Single(root.Literals);
@@ -349,7 +401,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
                 e => Assert.Same(endpoint1, e),
                 e => Assert.Same(endpoint2, e));
             Assert.Null(c1.Parameters);
-            Assert.Empty(c1.Literals);
+            Assert.Null(c1.Literals);
 
             var catchAll = a.CatchAll;
             Assert.Same(endpoint2, Assert.Single(catchAll.Matches));
@@ -373,7 +425,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
             Assert.Null(root.Parameters);
 
             var next = Assert.Single(root.Literals);
@@ -381,7 +433,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
 
             var a = next.Value;
             Assert.Same(endpoint2, Assert.Single(a.Matches));
-            Assert.Empty(a.Literals);
+            Assert.Null(a.Literals);
 
             var b1 = a.Parameters;
             Assert.Same(endpoint2, Assert.Single(a.Matches));
@@ -396,7 +448,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
                 e => Assert.Same(endpoint1, e),
                 e => Assert.Same(endpoint2, e));
             Assert.Null(c1.Parameters);
-            Assert.Empty(c1.Literals);
+            Assert.Null(c1.Literals);
 
             var catchAll = a.CatchAll;
             Assert.Same(endpoint2, Assert.Single(catchAll.Matches));
@@ -417,7 +469,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
             Assert.Null(root.Parameters);
 
             var next = Assert.Single(root.Literals);
@@ -440,7 +492,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var test2_true = test1_0.PolicyEdges[true];
             Assert.Same(endpoint1, Assert.Single(test2_true.Matches));
             Assert.Null(test2_true.NodeBuilder);
-            Assert.Empty(test2_true.PolicyEdges);
+            Assert.Null(test2_true.PolicyEdges);
         }
 
         [Fact]
@@ -462,7 +514,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
             Assert.Null(root.Parameters);
 
             var next = Assert.Single(root.Literals);
@@ -486,7 +538,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var test2_true = test1_0.PolicyEdges[true];
             Assert.Same(endpoint1, Assert.Single(test2_true.Matches));
             Assert.Null(test2_true.NodeBuilder);
-            Assert.Empty(test2_true.PolicyEdges);
+            Assert.Null(test2_true.PolicyEdges);
 
             var test1_1 = a.PolicyEdges[1];
             Assert.Empty(test1_1.Matches);
@@ -499,12 +551,12 @@ namespace Microsoft.AspNetCore.Routing.Matching
             test2_true = test1_1.PolicyEdges[true];
             Assert.Same(endpoint2, Assert.Single(test2_true.Matches));
             Assert.Null(test2_true.NodeBuilder);
-            Assert.Empty(test2_true.PolicyEdges);
+            Assert.Null(test2_true.PolicyEdges);
 
             var test2_false = test1_1.PolicyEdges[false];
             Assert.Same(endpoint3, Assert.Single(test2_false.Matches));
             Assert.Null(test2_false.NodeBuilder);
-            Assert.Empty(test2_false.PolicyEdges);
+            Assert.Null(test2_false.PolicyEdges);
         }
 
         [Fact]
@@ -526,7 +578,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
             Assert.Null(root.Parameters);
 
             var next = Assert.Single(root.Literals);
@@ -543,12 +595,12 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var test2_true = a.PolicyEdges[true];
             Assert.Equal(new[] { endpoint1, endpoint2, }, test2_true.Matches);
             Assert.Null(test2_true.NodeBuilder);
-            Assert.Empty(test2_true.PolicyEdges);
+            Assert.Null(test2_true.PolicyEdges);
 
             var test2_false = a.PolicyEdges[false];
             Assert.Equal(new[] { endpoint3, }, test2_false.Matches);
             Assert.Null(test2_false.NodeBuilder);
-            Assert.Empty(test2_false.PolicyEdges);
+            Assert.Null(test2_false.PolicyEdges);
         }
 
         [Fact]
@@ -570,7 +622,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
             Assert.Null(root.Parameters);
 
             var next = Assert.Single(root.Literals);
@@ -587,12 +639,12 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var test1_0 = a.PolicyEdges[0];
             Assert.Equal(new[] { endpoint1, }, test1_0.Matches);
             Assert.Null(test1_0.NodeBuilder);
-            Assert.Empty(test1_0.PolicyEdges);
+            Assert.Null(test1_0.PolicyEdges);
 
             var test1_1 = a.PolicyEdges[1];
             Assert.Equal(new[] { endpoint2, endpoint3, }, test1_1.Matches);
             Assert.Null(test1_1.NodeBuilder);
-            Assert.Empty(test1_1.PolicyEdges);
+            Assert.Null(test1_1.PolicyEdges);
         }
 
         [Fact]
@@ -614,7 +666,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
             Assert.Null(root.Parameters);
 
             var next = Assert.Single(root.Literals);
@@ -632,12 +684,12 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var test1_0 = a.PolicyEdges[0];
             Assert.Equal(new[] { endpoint1, }, test1_0.Matches);
             Assert.Null(test1_0.NodeBuilder);
-            Assert.Empty(test1_0.PolicyEdges);
+            Assert.Null(test1_0.PolicyEdges);
 
             var test1_1 = a.PolicyEdges[1];
             Assert.Equal(new[] { endpoint2, endpoint3, }, test1_1.Matches);
             Assert.Null(test1_1.NodeBuilder);
-            Assert.Empty(test1_1.PolicyEdges);
+            Assert.Null(test1_1.PolicyEdges);
 
             var nonRouteEndpoint = a.PolicyEdges[int.MaxValue];
             Assert.Equal("MaxValueEndpoint", Assert.Single(nonRouteEndpoint.Matches).DisplayName);
@@ -662,7 +714,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var root = builder.BuildDfaTree();
 
             // Assert
-            Assert.Empty(root.Matches);
+            Assert.Null(root.Matches);
             Assert.Null(root.Parameters);
 
             var next = Assert.Single(root.Literals);
@@ -671,7 +723,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             var a = next.Value;
             Assert.Equal(new[] { endpoint1, endpoint2, endpoint3, }, a.Matches);
             Assert.Null(a.NodeBuilder);
-            Assert.Empty(a.PolicyEdges);
+            Assert.Null(a.PolicyEdges);
         }
 
         [Fact]