Fix dotnet/aspnetcore#3634

Author: rynowak

src/Microsoft.AspNetCore.JsonPatch/Internal/ObjectVisitor.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections;
 using Microsoft.AspNetCore.JsonPatch.Adapters;
 using Newtonsoft.Json.Serialization;
 
@@ -56,6 +55,13 @@ public bool TryVisit(ref object target, out IAdapter adapter, out string errorMe
                     adapter = null;
                     return false;
                 }
+                
+                // If we hit a null on an interior segment then we need to stop traversing.
+                if (next == null)
+                {
+                    adapter = null;
+                    return false;
+                }
 
                 target = next;
                 adapter = SelectAdapter(target);

test/Microsoft.AspNetCore.JsonPatch.Test/IntegrationTests/SimpleObjectIntegrationTest.cs

@@ -2,6 +2,8 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Dynamic;
+using Microsoft.AspNetCore.JsonPatch.Exceptions;
 using Xunit;
 
 namespace Microsoft.AspNetCore.JsonPatch.IntegrationTests
@@ -124,5 +126,30 @@ public void AddReplacesGuid()
             Assert.Equal(newGuid, targetObject.GuidValue);
         }
 
+        // https://github.com/aspnet/AspNetCore/issues/3634
+        [Fact]
+        public void Regression_AspNetCore3634()
+        {
+            // Assert
+            var document = new JsonPatchDocument();
+            document.Move("/Object", "/Object/goodbye");
+
+            dynamic @object = new ExpandoObject();
+            @object.hello = "world";
+
+            var target = new Regression_AspNetCore3634_Object();
+            target.Object = @object;
+
+            // Act 
+            var ex = Assert.Throws<JsonPatchException>(() => document.ApplyTo(target));
+
+            // Assert
+            Assert.Equal("For operation 'move', the target location specified by path '/Object/goodbye' was not found.", ex.Message);
+        }
+
+        private class Regression_AspNetCore3634_Object
+        {
+            public dynamic Object { get; set; }
+        }
     }
 }

test/Microsoft.AspNetCore.JsonPatch.Test/Internal/ObjectVisitorTest.cs

@@ -205,6 +205,22 @@ public void Visit_DoesNotValidate_FinalPathSegment()
             Assert.IsType<PocoAdapter>(adapter);
         }
 
+        [Fact]
+        public void Visit_NullInteriorTarget_ReturnsFalse()
+        {
+            // Arrange
+            var visitor = new ObjectVisitor(new ParsedPath("/States/0"), new DefaultContractResolver());
+
+            // Act
+            object target = new Class1() { States = null, };
+            var visitStatus = visitor.TryVisit(ref target, out var adapter, out var message);
+
+            // Assert
+            Assert.False(visitStatus);
+            Assert.Null(adapter);
+            Assert.Null(message);
+        }
+
         [Fact]
         public void Visit_NullTarget_ReturnsNullAdapter()
         {