Fix for when multiple field implementations are all hidden

lib/graphql/schema/visibility/profile.rb

@@ -159,7 +159,7 @@ def field(owner, field_name)
                 end
               end
             end
-            visible_f.ensure_loaded
+            visible_f&.ensure_loaded
           elsif f && @cached_visible_fields[owner][f.ensure_loaded]
             f
           else

spec/graphql/schema/visibility/profile_spec.rb

@@ -32,4 +32,29 @@ class Query < GraphQL::Schema::Object
     loaded_type_names = query.types.loaded_types.map(&:graphql_name).reject { |n| n.start_with?("__") }.sort
     assert_equal ["Boolean", "Query", "String", "Thing"], loaded_type_names
   end
+
+
+  describe "when multiple field implementations are all hidden" do
+    class EnsureLoadedFixSchema < GraphQL::Schema
+      class BaseField < GraphQL::Schema::Field
+        def visible?(...)
+          false
+        end
+      end
+      class Query < GraphQL::Schema::Object
+        field_class(BaseField)
+
+        field :f1, String
+        field :f1, String
+      end
+
+      query(Query)
+      use GraphQL::Schema::Visibility
+    end
+
+    it "handles it without raising an error" do
+      result = EnsureLoadedFixSchema.execute("{ f1 }")
+      assert 1, result["errors"].size
+    end
+  end
 end