When you don't understand a warning or error, use diagnostics

$ perl -Mwarnings -le " my ( $l, $r ) = split /\s/, 'a b',2; print qq[
+$l$r\n]; "
ab


$ perl -Mwarnings -le " my ( $l, $r ) = split /\s/, 'a',2; print qq[$l
+$r\n]; "
Use of uninitialized value $r in concatenation (.) or string at -e lin
+e 1.
a


$ perl -Mdiagnostics -Mwarnings -le " my ( $l, $r ) = split /\s/, 'a',
+2; print qq[$l$r\n]; "
Use of uninitialized value $r in concatenation (.) or string at -e lin
+e 1 (#1)
    (W uninitialized) An undefined value was used as if it were alread
+y
    defined.  It was interpreted as a "" or a 0, but maybe it was a mi
+stake.
    To suppress this warning assign a defined value to your variables.

...*snip*...

a
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So maybe you assign a value to $SKU or temporarily disable that warning with

no warnings 'uninitialized';
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