    function baseMerge(object, source, srcIndex, customizer, stack) {
      if (object === source) {
        return;
      }
      baseFor(source, function(srcValue, key) {
        if (isObject(srcValue)) {
          stack || (stack = new Stack);
          baseMergeDeep(object, source, key, srcIndex, baseMerge, customizer, stack);
        }
        else {
          var newValue = customizer
            ? customizer(object[key], srcValue, (key + ''), object, source, stack)
            : undefined;

          if (newValue === undefined) {
            newValue = srcValue;
          }
          assignMergeValue(object, key, newValue);
        }
      }, keysIn);
    }