Allow empty email

This fixes a problem when updating the profile due to having a hidden email field.

app/models/user.rb

@@ -5,7 +5,8 @@ class User < ApplicationRecord
 
   validates :password, presence: true, length: { minimum: 6 }, allow_nil: true
   validates :name, uniqueness: { case_sensitive: false, message: "already in use" }, allow_nil: false
-  validates :email, uniqueness: { case_sensitive: false, message: "already in use" }, allow_nil: true
+  validates :email, uniqueness: { case_sensitive: false, message: "already in use" }, allow_nil: true, allow_blank: true
+
   validates :invitation_token, presence: true, on: :create
   validate :valid_invitation_token, on: :create