- scm_is_false (text) ? 0 : scm_to_wide_char_string (text),
- scm_is_false (tooltiptext) ? 0 : scm_to_wide_char_string (tooltiptext),
- scm_is_false (img) ? 0 : unwrap_texture (img),
- scm_is_false (pressedimg) ? 0 : unwrap_texture (pressedimg),
+ text == SCM_UNDEFINED ? 0 : scm_to_wide_char_string (text),
+ tooltiptext == SCM_UNDEFINED ? 0 : scm_to_wide_char_string (tooltiptext),
+ img == SCM_UNDEFINED ? 0 : unwrap_texture (img),
+ pressedimg == SCM_UNDEFINED ? 0 : unwrap_texture (pressedimg),