Prevent astNode is undefined for _entities & _service query

Author: hnq90

src/estimators/directive/index.ts

@@ -28,7 +28,8 @@ export default function (options?: {}): ComplexityEstimator {
   });
 
   return (args: ComplexityEstimatorArgs) => {
-    const values = getDirectiveValues(directive, args.field.astNode);
+    const astNode = (args.field && args.field.astNode) || {};
+    const values = getDirectiveValues(directive, astNode);
 
     // Ignore if no directive set
     if (!values) {