trivial: fix not-a-mapping pylint warning (#52732)

pylint.rc

@@ -32,7 +32,6 @@ disable=
     no-member,
     no-self-use,
     non-parent-init-called,
-    not-a-mapping,
     not-callable,
     possibly-unused-variable,
     protected-access,

wcs/wscalls.py

@@ -266,7 +266,7 @@ class NamedWsCall(XmlStorableObject):
             cache=True,
             notify_on_errors=self.notify_on_errors,
             record_on_errors=self.record_on_errors,
-            **self.request,
+            **(self.request or {}),
         )[2]
         return json_loads(data)