[amibroker] Why does this IF error ?

[gmorlosky]

I get an error about not being numeric for line # 2 below which I // out. Why 
is "if (fc > 20)" not valid ?

 fc = Foreign( symbol, "C" );
// if (fc > 20)
  if( ! IsNull( fc[ 0 ] ) )
  {
    Plot( 100 * ( fc - fc[ fvb ] )/ fc[ fvb ], symbol, colorLightOrange + ( 
(2*i) % 15 ), styleLine );
  }
// }