small refactor extracted from #4309

Author: yaacovCR

src/execution/execute.ts

@@ -299,10 +299,13 @@ export function executeQueryOrMutationOrSubscriptionEvent(
       variableValues,
       hideSuggestions,
     } = validatedExecutionArgs;
-    const rootType = schema.getRootType(operation.operation);
+
+    const { operation: operationType, selectionSet } = operation;
+
+    const rootType = schema.getRootType(operationType);
     if (rootType == null) {
       throw new GraphQLError(
-        `Schema is not configured to execute ${operation.operation} operation.`,
+        `Schema is not configured to execute ${operationType} operation.`,
         { nodes: operation },
       );
     }
@@ -312,7 +315,7 @@ export function executeQueryOrMutationOrSubscriptionEvent(
       fragments,
       variableValues,
       rootType,
-      operation.selectionSet,
+      selectionSet,
       hideSuggestions,
     );