sub _validate_operator {
my ($operator) = @_;
my %allowed_operators = map { $_ => 1 } qw(= != < > <= >= like -not_like -in -ident -bool -not_bool -or);
my %allowed_operators =
map { $_ => 1 } qw(= != < > <= >= like -not_like -in -ident -bool -not_bool -or -like -not -and -regexp);
Koha::Exceptions::REST::Query::InvalidOperator->throw( operator => $operator )
unless exists $allowed_operators{$operator};
return;
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