Not tested...

clean_sub_contractor_contracts.rb

class CleanSubContractorContracts 
  
  def records
    @records ||= SubContractorContract.includes(:contact).where("users.id IS  NULL")
  end
  
  def no_user
    @no_user ||= User.find_by_email('[email protected]')
  end
  
  def sub_contractor(contract)
    contract.sub_contractor
  end
  
  def first_authorized_signer(sub_contractor)
    return nil unless sub_contractor
    sub_contractor.authorized_signers.first
  end
  
  def best_user(contract)
    first_authorized_signer(sub_contractor(contract)) || no_user
  end
  
  def get_contacts
    records.each do |contract|
      contract.contact = best_user(contact)
    end
  end
  
  def save_records!
    get_contacts
    records.each do |record|
      record.save!
    end
  end
  
  def execute!
    SubContractorContracts.transaction do 
      save_records!
    end
  end
  
end