code: function loadIfExists(path, moduleStack, errMsg) {
          var servicesDir = this.injector.servicesDir;
          var servicesFullPath = this.injector.rootDir + '/' + servicesDir;
  
          // if the file doesn't exist, either throw an error (if msg passed in), else just return null
          if (!fs.existsSync(p.join(servicesFullPath, path + '.js'))) {
              if (errMsg) {
                  throw new Error(errMsg + ' ' + servicesFullPath + path + '.js');
              }
              else {
                  return null;
              }
          }
  
          // else load the module
          return this.injector.loadModule(servicesDir + path, moduleStack);
      }
docs: Load a module if it exists
  @param path
  @param moduleStack
  @param errMsg
  @returns {*}