[wxlua-users] wxlua does not properly report an error (crash instead)

How to reproduce:

change
    gridtable.GetTypeName = function( self, row, col )
        if col == Col_Id or col == Col_Priority then
            return wx.wxGRID_VALUE_NUMBER

to 
    gridtable.GetTypeName = function( self, row, col )
        if col == Col_Id or col == Col_Priority then
            return wx.wxEmptyString

I realize that this is not a type but this is purely to demonstrate the 
problem I found it in a more complex situation.

Returning '' will properly report the error it seems to be related to 
wx.wxEmptyString.

Hope someone can figure out how to fix the problem

Andre