[Bugfix] Fix KV Cache Spec CI Failure (#787)

Author: kyuyeunk

tpu_commons/worker/tpu_worker_jax.py

@@ -255,6 +255,9 @@ def get_kv_cache_spec(self) -> dict[str, KVCacheSpec]:
         # and the vLLM side should be updated to handle the translation.
         kv_cache_specs = self.model_runner.get_kv_cache_spec()
 
+        if len(kv_cache_specs) == 0:
+            return kv_cache_specs
+
         # TODO(kyuyeunk): Instead of checking page_size_bytes here, introduce
         # feature that allows overriding page_size_bytes of KVCacheSpec.
         vllm_page_size_bytes = get_uniform_page_size(kv_cache_specs)