MT#60400 /api/soundsets remove null search detection

* customer_id search param now has the same search logic
  as the rest as it had before 'null' detection and conversion
  => 'undef' whereas it's not needed anymore because it's now
  supported globally. The change also fixes an empty response
  issue.

Change-Id: If95de44d16ca2871da72d0ee019850802a3a94dd

lib/NGCP/Panel/Controller/API/SoundSets.pm

@@ -27,7 +27,7 @@ sub query_params {
             query => {
                 first => sub {
                     my $q = shift;
-                    return { 'me.contract_id' => lc($q) eq 'null' ? undef : $q };
+                    return { 'me.contract_id' => $q };
                 },
                 second => sub {},
             },