flowable/flowable-engine · error · FlowableIllegalArgumentException

comment is null

Error message

comment is null

What it means

SaveCommentCmd.execute validates the Comment passed in before persisting. Flowable throws FlowableIllegalArgumentException('comment is null') when the comment object itself is null, because there is nothing to save and the update would fail downstream. It is an argument-validation guard at the start of the command.

Source

Thrown at modules/flowable-engine/src/main/java/org/flowable/engine/impl/cmd/SaveCommentCmd.java:40

import org.flowable.engine.impl.persistence.entity.CommentEntityManager;
import org.flowable.engine.impl.util.CommandContextUtil;

/**
 * @author Tijs Rademakers
 */
public class SaveCommentCmd implements Command<Void>, Serializable {

    private static final long serialVersionUID = 1L;
    protected CommentEntity comment;

    public SaveCommentCmd(CommentEntity comment) {
        this.comment = comment;
    }

    @Override
    public Void execute(CommandContext commandContext) {
        if (comment == null) {
            throw new FlowableIllegalArgumentException("comment is null");
        }
        if (comment.getId() == null) {
            throw new FlowableIllegalArgumentException("comment id is null");
        } 
        
        CommentEntityManager commentEntityManager = CommandContextUtil.getCommentEntityManager(commandContext);
        
        String eventMessage = comment.getFullMessage().replaceAll("\\s+", " ");
        if (eventMessage.length() > 163) {
            eventMessage = eventMessage.substring(0, 160) + "...";
        }
        comment.setMessage(eventMessage);

        commentEntityManager.update(comment);

        return null;
    }
}

View on GitHub (pinned to d6d39ce1c6)

Solutions

1. Ensure a non-null Comment/CommentEntity is created or fetched before calling saveComment.
2. Check the code path that produced the comment for a null return (e.g. createComment result ignored).
3. If updating an existing comment, fetch it via getComment(id) and verify non-null first.

Example fix

// before
Comment comment = taskService.getComment(commentId); // may be null
comment.setFullMessage("updated");
taskService.saveComment(comment);
// after
Comment comment = taskService.getComment(commentId);
if (comment == null) {
    throw new IllegalStateException("Comment " + commentId + " not found");
}
comment.setFullMessage("updated");
taskService.saveComment(comment);

if (comment == null) { throw new IllegalArgumentException("comment must be non-null before saveComment"); }

if (comment instanceof Comment && comment != null) { /* safe to save */ }

try {
    taskService.saveComment(comment);
} catch (FlowableIllegalArgumentException e) {
    if (e.getMessage().contains("comment is null")) {
        comment = taskService.addComment(taskId, processInstanceId, message);
    }
}

When it happens

Trigger: Calling TaskService.saveComment(null) or executing SaveCommentCmd with a null comment reference.

Common situations: Comment loaded by id returned null (record deleted) and then passed to saveComment; a lookup helper returning null instead of a fresh CommentEntity.

Related errors

• comment id is null
• model is null
• categoryLike is null
• categoryNotEquals is null
• name is null

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/52f5525904d9e229. Report an issue: GitHub.