Use custom object formatters for any part of a diff, not just leaf nodes

src/core/matchers/NullDiffBuilder.js

@@ -4,7 +4,8 @@ getJasmineRequireObj().NullDiffBuilder = function(j$) {
       withPath: function(_, block) {
         block();
       },
-      record: function() {}
+      setRoots: function() {},
+      recordMismatch: function() {}
     };
   };
 };