Dear STATA community,

I run into error when I run ppmlhdfe with no independent variable. For example:

Code:
use "http://fmwww.bc.edu/RePEc/bocode/e/EXAMPLE_TRADE_FTA_DATA" if category=="TOTAL", clear
ppmlhdfe trade , absorb( isoexp isoimp )
The error is:
Code:
                  mean():  3301  subscript invalid
            GLM::solve():     -  function returned error
                 <istmt>:     -  function returned error
r(3301);
Does anyone else have the same problem? Any advice is much appreciated!