fix (socket) Use default socketclass if server has nil socketclass.

Author: Juha Suuraho

lib/net/ldap/connection.rb

@@ -22,7 +22,7 @@ def initialize(server = {})
     @instrumentation_service = server[:instrumentation_service]
 
     # Allows tests to parameterize what socket class to use
-    @socket_class = server.fetch(:socket_class, DefaultSocket)
+    @socket_class = server.fetch(:socket_class, DefaultSocket) || DefaultSocket
 
     yield self if block_given?
   end