class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  belongs_to :organisation

  def send_welcome_email
    UserMailer.welcome_email(self).deliver_now
  end
end

class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  belongs_to :organisation

  validates :first_name, :last_name, :email, presence: true
  validates_format_of :email,:with => /\A[^@\s]+@([^@\s]+\.)+[^@\s]+\z/

  def send_welcome_email
    UserMailer.welcome_email(self).deliver_now
  end
end

Add presence validations and email format validation
Add presence validations and email format validation
