Find bug

Hi, find a bug.

When Delete all rows and cols on Sheet Excel file, and this sheet get to SimpleXLSX, I have a error.

Uncaught exception 'Exception' with message 'Invalid cell index.' in
/DIR/simplexlsx.class.php:192

Stack trace:
#0 DIR/FILENAME(107): SimpleXLSX->_columnIndex(NULL)
#1 DIR/FILENAME(119): SimpleXLSX->dimension(2)
#2 DIR/FILENAME(245): SimpleXLSX->rows(2)
#3 XXXXXXX
#4 XXXXXXX

Resolve, diff:

106: $d = explode(':', $ref);
107:
108: if( is_null($d[1]) ) return false; // NEW RECORD FIX BUG
109:
110: $index = $this->_columnIndex( $d[1] );

thx, I'll add it next release

Hi Sergey,
Your code has been very helpful. Thank you very much.
I had this error too recently. When can we get the new release?
Thanks
Bruce

0.6.3