use method in validates statement

app/models/project.rb

@@ -162,7 +162,7 @@ class Project < ActiveRecord::Base
   validates :namespace, presence: true
   validates_uniqueness_of :name, scope: :namespace_id
   validates_uniqueness_of :path, scope: :namespace_id
-  validates :import_url, addressable_url: true, if: "import_url.present?"
+  validates :import_url, addressable_url: true, if: :external_import?
   validates :star_count, numericality: { greater_than_or_equal_to: 0 }
   validate :check_limit, on: :create
   validate :avatar_type,