If your file only contains one value, whay are you using a while to read it? Just use the diamond operator, <>:

$_ = <last_assignee>;
chomp;
if ($_ ne "") {
    $assignee_last = $_;
}
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As others have suggested, make sure you add strict and warnings, and use chomp rather than chop.

Finally, a question: Your if and the assignment to $assignee_last looks to me like a red flag, but it's hard to tell without seeing what follows. What does your program go on to do if $_ eq ""?