diff --git a/addons/api/mirage/config.js b/addons/api/mirage/config.js
index b7ff24208..cd4de1f31 100644
--- a/addons/api/mirage/config.js
+++ b/addons/api/mirage/config.js
@@ -632,23 +632,7 @@ function routes() {
       { queryParams: { credential_store_id: credentialStoreId } },
     ) => credentialLibraries.where({ credentialStoreId }),
   );
-  this.get(
-    '/credential-libraries/:id',
-    function ({ credentialLibraries }, { params: { id } }) {
-      const library = credentialLibraries.find(id);
-      // BE API only updates these fields if there's an update mask, otherwise they remain unmodified
-      // but we don't need this flow in our mocks, so we are deleting fields with null value
-      const { credentialMappingOverrides } = library;
-      if (Object.keys(credentialMappingOverrides || {}).length) {
-        Object.keys(credentialMappingOverrides).forEach((key) => {
-          if (credentialMappingOverrides[key] === null) {
-            delete credentialMappingOverrides[key];
-          }
-        });
-      }
-      return library;
-    },
-  );
+  this.get('/credential-libraries/:id');
   this.post(
     '/credential-libraries',
     function ({ credentialStores, credentialLibraries }) {
diff --git a/addons/api/mirage/serializers/credential-library.js b/addons/api/mirage/serializers/credential-library.js
index 1d1506f81..66146de29 100644
--- a/addons/api/mirage/serializers/credential-library.js
+++ b/addons/api/mirage/serializers/credential-library.js
@@ -14,6 +14,17 @@ export default ApplicationSerializer.extend({
       arguments,
     );
     json.credential_store_id = model.credentialStoreId;
+
+    // BE API only updates these fields if there's an update mask, otherwise they remain unmodified
+    // but we don't need this flow in our mocks, so we are deleting fields with null value
+
+    if (json.credential_mapping_overrides) {
+      Object.keys(json.credential_mapping_overrides).forEach((key) => {
+        if (json.credential_mapping_overrides[key] === null) {
+          delete json.credential_mapping_overrides[key];
+        }
+      });
+    }
     return json;
   },
 });