Allow forms for objects that don't respond to the "errors" method.

Useful for non-model forms, such as search forms.

lib/simple_form/components/errors.rb

@@ -32,7 +32,11 @@ def errors
       end
 
       def errors_on_attribute
-        object.errors[attribute_name]
+        if object.respond_to?(:errors)
+          object.errors[attribute_name]
+        else
+          []
+        end
       end
 
       def errors_on_association

test/components/error_test.rb

@@ -23,6 +23,13 @@ def with_error_for(object, attribute_name, type, options={}, &block)
     assert_no_select 'span.error'
   end
 
+  test "error should not generate messages when object doesn't respond to errors method" do
+    @user.instance_eval {undef errors}
+    with_error_for @user, :name, :string
+    assert_no_select 'span.error'
+  end
+
+
   test 'error should generate messages for attribute with single error' do
     with_error_for @user, :name, :string
     assert_select 'span.error', "can't be blank"