set email to nil instead of an empty string

app/models/person.rb

@@ -3,7 +3,7 @@
 # Represents a person in the system
 class Person < ApplicationRecord
   has_many :affiliations, dependent: :destroy
-  has_many :lter_roles, -> { where(['role_type_id = ?', RoleType.find_by(name: 'lter')]) },
+  has_many :lter_affiliations, -> { where(['role_type_id = ?', RoleType.find_by(name: 'lter')]) },
            source: :role, through: :affiliations
   has_many :lno_roles, -> { where(['role_type_id = ?', RoleType.find_by(name: 'lno')]) },
            source: :role, through: :affiliations
@@ -20,6 +20,7 @@ class Person < ApplicationRecord
   has_many :datatables, through: :data_contributions
 
   accepts_nested_attributes_for :affiliations, allow_destroy: true
+  accepts_nested_attributes_for :lter_affiliations, allow_destroy: true
 
   scope :by_sur_name, -> { order 'sur_name' }
   scope :by_sur_name_asc, -> { order 'sur_name ASC' }
@@ -64,6 +65,10 @@ def usa_address?
     country.blank? || country.casecmp('usa').zero? || country.casecmp('us').zero?
   end
 
+  def email=(val)
+    super(val == "" ? nil : val)
+  end
+
   def complete_address?
     !usa_address? ||
       (city.present? && street_address.present? &&