Merge branch 'cleanup' into 'NIFTy_6'

Tiny cleanup in Linearization.prepend_jac

See merge request !515

nifty6/linearization.py

@@ -65,10 +65,10 @@ class Linearization(Operator):
         return self.make_var(self._val, self._want_metric)
 
     def prepend_jac(self, jac):
-        metric = None
-        if self._metric is not None:
-            from .operators.sandwich_operator import SandwichOperator
-            metric = None if self._metric is None else SandwichOperator.make(jac, self._metric)
+        if self._metric is None:
+            return self.new(self._val, self._jac @ jac)
+        from .operators.sandwich_operator import SandwichOperator
+        metric = SandwichOperator.make(jac, self._metric)
         return self.new(self._val, self._jac @ jac, metric)
 
     @property