Make 'n' optional for search type history request

IPython/zmq/ipkernel.py

@@ -486,7 +486,7 b' class Kernel(Configurable):'
                                                         raw=raw, output=output)
 
         elif hist_access_type == 'search':
-            n = parent['content']['n']
+            n = parent['content'].get('n')
             pattern = parent['content']['pattern']
             hist = self.shell.history_manager.search(pattern, raw=raw,
                                                      output=output, n=n)