simplify nil handling

app/models/gpg_key.rb

@@ -46,8 +46,7 @@ class GpgKey < ActiveRecord::Base
   end
 
   def key=(value)
-    value.strip! unless value.blank?
-    write_attribute(:key, value)
+    super(value&.strip)
   end
 
   def user_infos

spec/models/gpg_key_spec.rb

@@ -44,6 +44,10 @@ describe GpgKey do
 
       expect(described_class.new(key: " #{key} ").key).to eq(key)
     end
+
+    it 'does not strip when the key is nil' do
+      expect(described_class.new(key: nil).key).to be_nil
+    end
   end
 
   describe '#user_infos' do