didi/DoKit · error · IllegalArgumentException

RequestHandler must not be null.

Error message

RequestHandler must not be null.

What it means

DokitPicasso.Builder.addRequestHandler() throws IllegalArgumentException when passed a null RequestHandler. Request handlers resolve custom URI schemes (contacts, video thumbnails, etc.), so null is never valid. Fail-fast null guard.

Source

Thrown at Android/dokit/src/main/java/com/didichuxing/doraemonkit/picasso/DokitPicasso.java:791

     * <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.");
      }
      if (this.transformer != null) {
        throw new IllegalStateException("Transformer already set.");
      }
      this.transformer = transformer;
      return this;
    }

    /** Register a {@link RequestHandler}. */
    public Builder addRequestHandler(RequestHandler requestHandler) {
      if (requestHandler == null) {
        throw new IllegalArgumentException("RequestHandler must not be null.");
      }
      if (requestHandlers == null) {
        requestHandlers = new ArrayList<RequestHandler>();
      }
      if (requestHandlers.contains(requestHandler)) {
        throw new IllegalStateException("RequestHandler already registered.");
      }
      requestHandlers.add(requestHandler);
      return this;
    }

    /**
     * @deprecated Use {@link #indicatorsEnabled(boolean)} instead.
     * Whether debugging is enabled or not.
     */
    @Deprecated public Builder debugging(boolean debugging) {
      return indicatorsEnabled(debugging);
    }

View on GitHub (pinned to 626827cddb)

Solutions

1. Pass a non-null RequestHandler instance
2. Filter nulls out of the handler list before registering: handlers.removeAll(Collections.singleton(null))
3. Fix the factory/DI provider so it returns a real handler

Example fix

// before
for (RequestHandler h : handlers) {
  builder.addRequestHandler(h); // IllegalArgumentException if h == null
}

// after
for (RequestHandler h : handlers) {
  if (h != null) builder.addRequestHandler(h);
}

for (RequestHandler h : handlers) { if (h != null) builder.addRequestHandler(h); }

boolean isRegistrableHandler(RequestHandler h) { return h != null; }

When it happens

Trigger: Calling builder.addRequestHandler(null), typically from a list of handlers that contains a null entry or an uninitialized handler field.

Common situations: Iterating a handler list built conditionally where one branch added null; handler instances created by reflection or DI that failed silently.

Related errors

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

AI-assisted analysis of didi/DoKit@626827cddb (2026-08-14). Data as JSON: /api/errors/ea31de55f3daf221. Report an issue: GitHub.