Fix graphql doc generation for interfaces

Remove extra empty lines from generated doc when interface
has no fields.

app/assets/javascripts/work_items/graphql/work_item_by_iid.query.graphql

@@ -6,7 +6,7 @@ query workItemByIid($fullPath: ID!, $iid: String) {
       id
       workItems(iid: $iid) {
         nodes {
-          ... WorkItem
+          ...WorkItem
         }
       }
     }
@@ -16,7 +16,7 @@ query workItemByIid($fullPath: ID!, $iid: String) {
       descriptionHtml
       workItems(iid: $iid) {
         nodes {
-          ... WorkItem
+          ...WorkItem
         }
       }
     }

app/assets/javascripts/work_items/index.js

@@ -23,7 +23,7 @@ export const initWorkItemsRoot = () => {
     savedRepliesNewPath,
   } = el.dataset;
   const routePrefix = parseBoolean(isGroup) ? 'groups' : '';
-  const basePath =  joinPaths(routePrefix, el.dataset.fullPath);
+  const basePath = joinPaths(routePrefix, el.dataset.fullPath);
 
   return new Vue({
     el,

doc/api/graphql/reference/index.md

@@ -27115,8 +27115,6 @@ Implementations:
 - [`Group`](#group)
 - [`ProjectNamespace`](#projectnamespace)
-
-
 #### `NoteableInterface`
 Implementations:

tooling/graphql/docs/templates/default.md.haml

@@ -208,8 +208,9 @@
   - type[:implemented_by].each do |type_name|
     ~ "- [`#{type_name}`](##{type_name.downcase})"
   \
-  = render_object_fields(type[:fields], owner: type, level_bump: 1)
-  \
+  - unless type[:fields].blank?
+    = render_object_fields(type[:fields], owner: type, level_bump: 1)
+    \
 
 :plain
   ## Input types