s/(?:)// will do nothing (or rather, replace one-zero length string with another zero-length string). So, if you have a possibly-empty pattern in a variable, you could use

s/(?:$pat)//
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or

my $re = qr/$pat/;

s/$re//
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The latter was buggy before 5.18 as it resulted in the same as s/// when $pat contained an empty string.

glad to learn that there is a way to suppress the urge of abnormal behavior.