Do not add controls when it is empty. Fixed #17

Some LDAP servers, such as ApacheDS, consider as invalid protocol, if controls
is an empty array.

Author: doitian

lib/net/ldap.rb

@@ -1389,9 +1389,9 @@ def search(args = {})
           false.to_ber,
           rfc2696_cookie.map{ |v| v.to_ber}.to_ber_sequence.to_s.to_ber
         ].to_ber_sequence if paged_searches_supported
-      controls = controls.to_ber_contextspecific(0)
+      controls = controls.empty? ? nil : controls.to_ber_contextspecific(0)
 
-      pkt = [next_msgid.to_ber, request, controls].to_ber_sequence
+      pkt = [next_msgid.to_ber, request, controls].compact.to_ber_sequence
       @conn.write pkt
 
       result_code = 0