ltext( pos=NULL )

ltext( 0, 0, pos=NULL, label="xxxx")
gives an error message.

The help page of ``ltext'' references to the help page of ``text''
where the default value of pos is set to NULL.

To solve the problem ``ltext'' could be changed:
OLD:
    if (!missing(pos))
NEW:
    if (!missing(pos) && ! is.null(pos) )

Wolfram