Fixes #946

src/registry/mod.rs

@@ -606,20 +606,7 @@ impl Registry {
             })
             .collect();
 
-        if !possible_types.is_empty() {
+        if let MetaType::Object { fields, .. } = self.types.get_mut(&self.query_type).unwrap() {
-            self.types.insert(
-                "_Entity".to_string(),
-                MetaType::Union {
-                    name: "_Entity".to_string(),
-                    description: None,
-                    possible_types,
-                    visible: None,
-                    rust_typename: "async_graphql::federation::Entity",
-                },
-            );
-
-            let query_root = self.types.get_mut(&self.query_type).unwrap();
-            if let MetaType::Object { fields, .. } = query_root {
             fields.insert(
                 "_service".to_string(),
                 MetaField {
@@ -636,7 +623,21 @@ impl Registry {
                     compute_complexity: None,
                 },
             );
+        }
 
+        if !possible_types.is_empty() {
+            self.types.insert(
+                "_Entity".to_string(),
+                MetaType::Union {
+                    name: "_Entity".to_string(),
+                    description: None,
+                    possible_types,
+                    visible: None,
+                    rust_typename: "async_graphql::federation::Entity",
+                },
+            );
+
+            if let MetaType::Object { fields, .. } = self.types.get_mut(&self.query_type).unwrap() {
                 fields.insert(
                     "_entities".to_string(),
                     MetaField {