Fix NoneType object has no attribute zero_

ktransformers/models/custom_cache.py

@@ -172,7 +172,8 @@ class StaticCache(transformers.StaticCache):
         for layer_idx in range(len(self.key_cache)):
             # In-place ops prevent breaking the static address
             self.key_cache[layer_idx].zero_()
-            self.value_cache[layer_idx].zero_()
+            if self.value_cache[layer_idx] is not None:
+                self.value_cache[layer_idx].zero_()
     
     def get_max_cache_shape(self) -> Tuple[int, int, int, int]:
         """Returns the maximum shape of the cache."""