Error when attaching a field form in a subform

Hi,

When attaching a field form with field_attach_form inside a subform I'm getting this ugly error:

Recoverable fatal error: Argument 1 passed to drupal_array_get_nested_value() must be an array, boolean given, called in date_api_elements.inc on line 307 and defined in drupal_array_get_nested_value() (line 6341 of includes/common.inc)

I think this is because the input element gets a value of FALSE with fields when form API is expecting an array, I'm attaching a proposed solution for this.