在项目问题上安装gulp

Question

我正在尝试将gulp安装到我的项目文件夹中。但是当我运行此命令来安装gulp时，我得到以下错误：

Sab-MacBook-Pro:myproject sab$ npm install gulp -save-dev
npm ERR! Darwin 14.5.0
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "install" "gulp" "-save-dev"
npm ERR! node v5.3.0
npm ERR! npm  v3.3.12
npm ERR! path /Users/sab/RubymineProjects/myproject/node_modules/gulp
npm ERR! code ENOTEMPTY
npm ERR! errno -66
npm ERR! syscall rename

npm ERR! ENOTEMPTY: directory not empty, rename '/Users/sab/RubymineProjects/myproject/node_modules/gulp' -> '/Users/sab/RubymineProjects/myproject/node_modules/.gulp.DELETE'
npm ERR! 
npm ERR! If you need help, you may report this error at:
npm ERR!     <https://github.com/npm/npm/issues>

npm ERR! Please include the following file with any support request:
npm ERR!     /Users/sab/RubymineProjects/myproject/npm-debug.log
Sab-MacBook-Pro:myproject sab$ 

如果我没错，错误信息是由于现有的gulp文件夹。但是当我查看我的项目node_module文件夹时，gulp文件夹不在那里。