Given the function below, provide the fix so error does not appear:

$>$ printmessage $<-$ function$($x$)\{$

$+$ if$($x $>0)$

$+$ print$("$x is greater than zero"$)$

$+$ else

$+$ print$("$x is less than or equal to zero"$)$

$+$ invisible$($x$)$

$+\}$

But when we call:

$>$ printmessage$($NA$)$

Error in if $($x $>0)$ print$("$x is greater than zero"$)$ else print$("$x is less than or equal to zero"$)$: missing value where TRUE$/$FALSE needed