Yes, it's annoying, but once you are aware of it (and get used to it), it's not so tough. Here's a simple demo of the basic pattern:

#!/usr/bin/perl -w

$_ = undef;
if ( 1 == 2 ) {  # this is line 4
  print "This cannot happen\n";
}
elsif ( $_ < 3 ) {  # the problem is at line 7
  print "This works okay (but throws a warning)\n";
}
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You'll see that the warning message cites line 4. Simple rule: when a warning points to an "if" statement and makes no sense for that line, check each of the "elsif" statements that relate to that line.