a variable can be empty (value is undef)

<nit>

The string could be undefined or defined and contain a zero-length string before we move on to containing only spaces or some other text.

$ perl -Mstrict -wE '
> sub grok
> {
>     my $str = shift;
>     say
>        defined $str
>        ? $str
>          ? qq{>$str<: defined and true}
>          : qq{>$str<: defined but not true}
>        : qq{>$str<: undefined};
> }
> 
> my $str;
> grok( $str );
> $str = q{};
> grok( $str );
> $str = q{   };
> grok( $str );
> $str .= q{ABC};
> grok( $str );'
Use of uninitialized value $str in concatenation (.) or string at -e l
+ine 5.
><: undefined
><: defined but not true
>   <: defined and true
>   ABC<: defined and true
$
[download]

</nit>

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