code: function(labelPositionArgs, defaultLabelPositionArgs) {
  
          if (labelPositionArgs === null) return null;
          if (labelPositionArgs === undefined) {
  
              if (defaultLabelPositionArgs === null) return null;
              return defaultLabelPositionArgs;
          }
  
          return joint.util.merge({}, defaultLabelPositionArgs, labelPositionArgs);
      }
docs: merge default label position args into label position args keep `undefined` or `null` because `{}` means something else