After getting the request for proposal, supervisors field check for the invalid emails.
Expected behavior: The given email is checked across the database and return the supervisor list. If those emails are valid, the control goes to else condition and creating proposal document takes place. If those emails are invalid, it assigns empty array to supervisors and the supervisors are checked if empty, If empty, it should return "invalid email"
Actual behavior: If random email id is given, the control goes to else condition in the proposal controller api.