Validation Error with Mongoose

POST URL - http://localhost:3000/api/v1/users
Body - email:sanjeevkarani@gmail.com

I am using mongodb latest & node v7.8.0

MongooseError: User validation failed
at ValidationError (/home/yashkarani/Desktop/workspace/samples/nodejs/yanb/node_modules/mongoose/lib/error/validation.js:27:11)
at model.Document.invalidate (/home/yashkarani/Desktop/workspace/samples/nodejs/yanb/node_modules/mongoose/lib/document.js:1604:32)
at /home/yashkarani/Desktop/workspace/samples/nodejs/yanb/node_modules/mongoose/lib/document.js:1476:17
at validate (/home/yashkarani/Desktop/workspace/samples/nodejs/yanb/node_modules/mongoose/lib/schematype.js:760:7)
at /home/yashkarani/Desktop/workspace/samples/nodejs/yanb/node_modules/mongoose/lib/schematype.js:805:11
at Array.forEach (native)
at SchemaString.SchemaType.doValidate (/home/yashkarani/Desktop/workspace/samples/nodejs/yanb/node_modules/mongoose/lib/schematype.js:765:19)
at /home/yashkarani/Desktop/workspace/samples/nodejs/yanb/node_modules/mongoose/lib/document.js:1474:9
at _combinedTickCallback (internal/process/next_tick.js:73:7)
at process._tickCallback (internal/process/next_tick.js:104:9)