Fix OpenSSL error with empty string reported in #1

Author: atyndall

lib/kms_rails/active_record.rb

@@ -20,7 +20,7 @@ def kms_attr(field, key_id:, retain: false, msgpack: false, context_key: nil, co
         enc = Core.new(key_id: key_id, msgpack: msgpack, context_key: context_key, context_value: context_value)
 
         define_method "#{field}=" do |data|
-          if data.nil? # Just set to nil if nil
+          if data.blank? # Just set to nil if nil
             clear_retained(field)
             self[real_field] = nil
             return 

spec/kms_rails/active_record_spec.rb

@@ -164,6 +164,11 @@
         subject.the_secret = 'foo'
         expect { subject.the_secret = nil }.to change { subject['the_secret_enc'] }.to(nil)
       end
+
+      it 'sets the field to nil if called with empty string' do
+        subject.the_secret = 'foo'
+        expect { subject.the_secret = '' }.to change { subject['the_secret_enc'] }.to(nil)
+      end
     end
 
     context '#the_secret' do