Problem/Motivation
form_type_textarea_value() behaves differently than form_type_textfield_value(), it does not ignore input that is set to NULL instead of FALSE. Example: if you have a body field on a node with a textarea element and you set the #type to 'hidden' on the outer field form element, then _form_builder_handle_input_element() will invoke the value_callback form_type_textarea_value() with input set to NULL.
Proposed resolution
Make form_type_textarea_value() behave the same as form_type_textfield_value() and ignore NULL input.
Remaining tasks
Review patch, write tests
User interface changes
none.
API changes
none.
