Error while trying to save document in MongoDB - node.js

Question

I have this signup method to save a user.
exports.signup = function(req, res) {
// Initialize the variables
var user = new User(req.body);
var message = null;
user.provider = 'local';
// save the user
user.save(function(err) {
if (err) {
console.log(err);
return res.status(400).send({
message: errorHandler.getErrorMessage(err)
});
} else {
req.login(user, function(err) {
if (err) {
res.status(400).send(err);
} else {
res.json(user);
}
});
}
});
};
Her is my Schema.
var UserSchema = new Schema({
name: {
type: String,
required: true
},
email: {
type: String,
index: true,
match: [/.+\#.+\..+/, "Please fill valid e-mail address"]
},
username: {
type: String,
trim: true,
unique: "Username should be unique",
required: true
},
password: {
type: String,
validate: [
function (password) {
return password && password.length > 6;
},
"Password should be greater than six letters"
]
},
salt: {
type: String
},
provider: {
type: String,
required: "Provider is required"
},
providerId: String,
providerData: {},
created: {
type: Date,
default: Date.now()
}
});
When I make a post request in an empty collection, the first is saved, but after that i am getting this error.
MongoError: Projection cannot have a mix of inclusion and exclusion.
at Function.MongoError.create (/home/sinnedde/WebstormProjects/mean-chatapp/node_modules/mongodb-core/lib/error.js:31:11)
at queryCallback (/home/sinnedde/WebstormProjects/mean-chatapp/node_modules/mongodb-core/lib/cursor.js:212:36)
at /home/sinnedde/WebstormProjects/mean-chatapp/node_modules/mongodb-core/lib/connection/pool.js:455:18
at _combinedTickCallback (internal/process/next_tick.js:67:7)
at process._tickCallback (internal/process/next_tick.js:98:9)
POST /signup 500 1445.231 ms - 615
Please help.
First req.body
{
"name":"John",
"email": "johndoe#gmail.com",
"username": "john123",
"password": "password"
}
Second req.body
{
"name":"Jane",
"email": "janedoe#gmail.com",
"username": "jane123",
"password": "password"
}