Added test for { a: null }

Author: glen-84

src/HotChocolate/Core/test/Types.Tests/Types/OneOfIntegrationTests.cs

@@ -34,6 +34,18 @@ public async Task A_is_null_and_B_is_set_Error()
             .MatchSnapshotAsync();
     }
 
+    [Fact]
+    public async Task A_is_null_Error()
+    {
+        // Error: Value for member field {a} must be non-null
+        await new ServiceCollection()
+            .AddGraphQL()
+            .AddQueryType<Query>()
+            .ModifyOptions(o => o.EnableOneOf = true)
+            .ExecuteRequestAsync("{ example(input: { a: null }) }")
+            .MatchSnapshotAsync();
+    }
+
     [Fact]
     public async Task B_is_set_Valid()
     {

src/HotChocolate/Core/test/Types.Tests/Types/__snapshots__/OneOfIntegrationTests.A_is_null_Error.snap

@@ -0,0 +1,21 @@
+{
+  "errors": [
+    {
+      "message": "The OneOf Input Object `ExampleInput` requires that exactly one field must be supplied and that field must not be `null`.",
+      "locations": [
+        {
+          "line": 1,
+          "column": 18
+        }
+      ],
+      "path": [
+        "example"
+      ],
+      "extensions": {
+        "type": "ExampleInput",
+        "specifiedBy": "https://spec.graphql.org/draft/#sec-OneOf-Input-Objects-Have-Exactly-One-Field",
+        "rfc": "https://github.com/graphql/graphql-spec/pull/825"
+      }
+    }
+  ]
+}