credstash lookup plugin: error out in run function when credstash not installed, not at module scope

lib/ansible/plugins/lookup/credstash.py

@@ -29,13 +29,12 @@ except ImportError:
     CREDSTASH_INSTALLED = False
 
 
-if not CREDSTASH_INSTALLED:
-    raise AnsibleError('The credstash lookup plugin requires credstash to be installed.')
-
-
 class LookupModule(LookupBase):
     def run(self, terms, variables, **kwargs):
 
+        if not CREDSTASH_INSTALLED:
+            raise AnsibleError('The credstash lookup plugin requires credstash to be installed.')
+
         if isinstance(terms, basestring):
             terms = [terms]