$subprefix never initialized

On line 346, within the function addnode_widget, _add_subform is invoked in the following manner:

_add_subform($form, $subform, $fieldname, $atype, $subprefix, $usesuffix, $weight);

However, the variable $subprefix is never initialized in the function. The variable $prefix, on the other hand, is initialized but not passed as one of these parameters.

Furthermore, in the function _add_subform itself, the passed $subprefix variable is never used.

I am leaving this as a minor bug, I don't know yet (just started working with module) if this is significant. Would like you to comment.