sub test {
    my ($self, @args) = @_;
    my %params;

    if (@args > 1) {
        %params = @args; # Will warn if @args has an odd number of elements
    } else {
        ... # Handle single argument
    }
}

##</code><code>##

test ({this => 1, that => 2});

sub test {
    my ($self, $args) = @_;
    my %params;

    if ('HASH' eq ref $args) {
        %params = %$args;
    } else {
        ... # Handle single argument
    }
}