jax-ml/jax · error · ValueError

key cannot be empty

Error message

key cannot be empty

What it means

LRUCache.get validates that the cache key is non-empty before building the cache file path; an empty (or falsy) key would map to a degenerate filename, so it raises ValueError. Keys are hashed strings naming compilation-cache entries.

Source

Thrown at jax/_src/lru_cache.py:94

      self.lock_timeout_secs = lock_timeout_secs

      self.lock_path = self.path / ".lockfile"
      if _is_local_filesystem(path):
        self.lock = filelock.FileLock(self.lock_path)
      else:
        self.lock = filelock.SoftFileLock(self.lock_path)

  def get(self, key: str) -> bytes | None:
    """Retrieves the cached value for the given key.

    Args:
      key: The key for which the cache value is retrieved.

    Returns:
      The cached data as bytes if available; ``None`` otherwise.
    """
    if not key:
      raise ValueError("key cannot be empty")

    cache_path = self.path / f"{key}{_CACHE_SUFFIX}"

    if self.eviction_enabled:
      self.lock.acquire(timeout=self.lock_timeout_secs)

    try:
      if not cache_path.exists():
        logger.debug(f"Cache miss for key: {key!r}")
        return None

      logger.debug(f"Cache hit for key: {key!r}")

      val = cache_path.read_bytes()

      if self.eviction_enabled:
        timestamp = time.time_ns().to_bytes(8, "little")
        atime_path = self.path / f"{key}{_ATIME_SUFFIX}"

View on GitHub (pinned to 1e1c6a8fc0)

Solutions

1. Ensure the key is a non-empty string (typically a hash hex digest) before calling get
2. If generating keys yourself, fall back to a stable hash of the empty input

Example fix

# before
value = cache.get(key if key else '')

# after
value = cache.get(key) if key else None

assert isinstance(key, str) and key, 'cache key must be a non-empty string'

def is_valid_key(k) -> bool:
    return isinstance(k, str) and len(k) > 0

When it happens

Trigger: Calling cache.get('') or cache.get(None) on a jax._src.lru_cache.LRUCache; indirectly if user code computes a cache key from strings that can be empty.

Common situations: Custom wrappers around the compilation cache that derive keys from possibly-empty names/paths; only hit by internal or advanced users of jax._src.lru_cache.

Related errors

• numpy masked arrays are not supported as direct inputs to JA
• Invalid compute type {c_type}. Current supported values are
• numpy masked arrays are not supported as direct inputs to JA
• Mesh axis names cannot be None. Got: {axis_names}
• Mesh requires the ndim of its first argument (`devices`) to

AI-assisted analysis of jax-ml/jax@1e1c6a8fc0 (2026-08-27). Data as JSON: /api/errors/6994164ba4588950. Report an issue: GitHub.