Only obfuscate if the instance has the field in question.

lib/polo/translator.rb

@@ -38,8 +38,9 @@ def obfuscate!(instances, fields)
         next if intersection(instance.attributes.keys, fields).empty?
 
         fields.each do |field, strategy|
-          value = instance.attributes[field.to_s] || ''
-          instance.send("#{field}=", new_field_value(field, strategy, value))
+          if value = instance.attributes[field.to_s]
+            instance.send("#{field}=", new_field_value(field, strategy, value))
+          end
         end
       end
     end

spec/polo_spec.rb

@@ -88,6 +88,20 @@
 
         expect(inserts).to eq [ %q{INSERT INTO "chefs" ("id", "name", "email") VALUES (1, 'Netto', 'changeme')} ]
       end
+
+      it 'only scrambles instances with the obfuscate field defined' do
+        Polo.configure do
+          obfuscate :name,
+                    email: ->(e) { "#{e.split("@")[0]}[email protected]" },
+                    title: ->(t) { t.chars.reverse!.join }
+        end
+
+        exp = Polo.explore(AR::Chef, 1, :recipes)
+
+        explore_statement = exp.join(';')
+        expect(explore_statement).to_not match('[email protected]')
+        expect(explore_statement).to_not match('Netto')
+      end
     end
 
     describe 'on_duplicate' do