return None kernel_spec if kernel_name not set

Author: rgbkrk

jupyter_client/manager.py

@@ -77,7 +77,7 @@ def _kernel_name_changed(self, name, old, new):
 
     @property
     def kernel_spec(self):
-        if self._kernel_spec is None:
+        if self._kernel_spec is None and self.kernel_name is not '':
             self._kernel_spec = self.kernel_spec_manager.get_kernel_spec(self.kernel_name)
         return self._kernel_spec