Backport Adapter#ldap_search from EE

lib/gitlab/ldap/adapter.rb

@@ -64,7 +64,7 @@ module Gitlab
                              end
         end
 
-        entries = ldap.search(options).select do |entry|
+        entries = ldap_search(options).select do |entry|
           entry.respond_to? config.uid
         end
 
@@ -77,6 +77,22 @@ module Gitlab
         users(*args).first
       end
 
+      def ldap_search(*args)
+        results = ldap.search(*args)
+
+        if results.nil?
+          response = ldap.get_operation_result
+
+          unless response.code.zero?
+            Rails.logger.warn("LDAP search error: #{response.message}")
+          end
+
+          []
+        else
+          results
+        end
+      end
+
       private
 
       def config