didi/DoKit · error · IllegalArgumentException

Listener must not be null.

Error message

Listener must not be null.

What it means

DokitPicasso.Builder.listener() throws IllegalArgumentException when passed a null Listener. The listener receives callbacks for failed image loads, so it must be a real object. This is a fail-fast null guard.

Source

Thrown at Android/dokit/src/main/java/com/didichuxing/doraemonkit/picasso/DokitPicasso.java:762

      return this;
    }

    /** Specify the memory cache used for the most recent images. */
    public Builder memoryCache(Cache memoryCache) {
      if (memoryCache == null) {
        throw new IllegalArgumentException("Memory cache must not be null.");
      }
      if (this.cache != null) {
        throw new IllegalStateException("Memory cache already set.");
      }
      this.cache = memoryCache;
      return this;
    }

    /** Specify a listener for interesting events. */
    public Builder listener(Listener listener) {
      if (listener == null) {
        throw new IllegalArgumentException("Listener must not be null.");
      }
      if (this.listener != null) {
        throw new IllegalStateException("Listener already set.");
      }
      this.listener = listener;
      return this;
    }

    /**
     * Specify a transformer for all incoming requests.
     * <p>
     * <b>NOTE:</b> This is a beta feature. The API is subject to change in a backwards incompatible
     * way at any time.
     */
    public Builder requestTransformer(RequestTransformer transformer) {
      if (transformer == null) {
        throw new IllegalArgumentException("Transformer must not be null.");
      }

View on GitHub (pinned to 626827cddb)

Solutions

1. Pass a non-null Listener implementation
2. Guard the call: only invoke listener() when you have a real listener to install
3. If no callbacks are needed, omit listener() entirely

Example fix

// before
Listener l = buildConfigDebug ? new DebugListener() : null;
builder.listener(l); // IllegalArgumentException in release

// after
if (buildConfigDebug) {
  builder.listener(new DebugListener());
}

if (listener != null) { builder.listener(listener); }

When it happens

Trigger: Calling builder.listener(null), commonly from an optional debug listener that was left unset in release builds.

Common situations: Debug-only listener wrapped in an if (BuildConfig.DEBUG) block whose variable is null in release; a listener reference from an uninitialized field.

Related errors

• Executor service must not be null.
• Memory cache must not be null.
• Transformer must not be null.
• RequestHandler must not be null.
• Downloader already set.

AI-assisted analysis of didi/DoKit@626827cddb (2026-08-14). Data as JSON: /api/errors/f4d76d4039112422. Report an issue: GitHub.