Query error on import range [duplicate]

I am importing data from another sheet. I am trying to not import rows that have a null value in a specific column. But no matter what I do it still imports the null row.

=QUERY(IMPORTRANGE("14ZDhy0VE-u0srsp1EZG6KaxMOusF8TzCcD2yWxPoxM0", "Hot Rolled Mild Steel!B2:H"),"where Col6 is not NULL")

This is column 6 from the sheet that is being imported as it may seem as column 5 here, I am not importing column1.