Bugfix: Treat operation name with empty string as null (graphql-dotnet#4078)

* Fix issue 4077

* Update

* update

Author: Shane32

src/GraphQL.Tests/Bugs/Bug1772.cs

@@ -26,7 +26,6 @@ public async Task DocumentExecuter_works_for_valid_operation(string? operationNa
     }
 
     [Theory]
-    [InlineData("")]
     [InlineData("thirdQuery")]
     [InlineData("query")]
     [InlineData("test")]

src/GraphQL.Tests/Bugs/Bug4078.cs

@@ -0,0 +1,37 @@
+using GraphQL.Types;
+
+namespace GraphQL.Tests.Bugs;
+
+// https://github.com/graphql-dotnet/graphql-dotnet/pull/4078
+public class Bug4078
+{
+    [Fact]
+    public async Task empty_string_for_operation_name_is_treated_as_null()
+    {
+        var schema = new Schema { Query = new QueryGraphType() };
+
+        var response = await schema.ExecuteAsync(_ =>
+        {
+            // to trigger the bug, the document must contain a named operation,
+            _.Query = "query abc { test }";
+            // along with an empty string for the operation name
+            _.OperationName = "";
+        });
+
+        response.ShouldBeCrossPlatJson("""
+            {
+                "data": {
+                    "test": "abc"
+                }
+            }
+            """);
+    }
+
+    public class QueryGraphType : ObjectGraphType
+    {
+        public QueryGraphType()
+        {
+            Field<StringGraphType>("test").Resolve(ctx => "abc");
+        }
+    }
+}

src/GraphQL.Tests/Bugs/Issue4075.cs

@@ -1,7 +1,7 @@
 using System.Numerics;
 using GraphQL.Types;
 
-namespace GraphQL.Tests.Bugs.Bug1046;
+namespace GraphQL.Tests.Bugs;
 
 public class Issue4075
 {

src/GraphQL/Execution/DocumentExecuter.cs

@@ -324,7 +324,7 @@ protected virtual ExecutionContext BuildExecutionContext(ExecutionOptions option
     /// <exception cref="NoOperationError">Thrown when the document does not include any operations.</exception>
     protected virtual GraphQLOperationDefinition GetOperation(string? operationName, GraphQLDocument document)
     {
-        if (operationName == null)
+        if (string.IsNullOrEmpty(operationName))
         {
             GraphQLOperationDefinition? match = null;
             foreach (var def in document.Definitions)
@@ -346,7 +346,7 @@ protected virtual GraphQLOperationDefinition GetOperation(string? operationName,
                 return op;
         }
 
-        throw new InvalidOperationNameError(operationName);
+        throw new InvalidOperationNameError(operationName!);
     }
 
     /// <summary>