flowable/flowable-engine · error · FlowableIllegalArgumentException

userId is null

Error message

userId is null

What it means

CreateMembershipCmd.execute(CommandContext) throws FlowableIllegalArgumentException when its userId field is null at execution time. A membership links a user to a group, and creating one without a user is invalid. Note the constructor only validates groupId here, so a null userId surfaces when the command runs.

Source

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

/**
 * @author Tom Baeyens
 */
public class CreateMembershipCmd implements Command<Object>, Serializable {

    private static final long serialVersionUID = 1L;

    String userId;
    String groupId;

    public CreateMembershipCmd(String userId, String groupId) {
        this.userId = userId;
        this.groupId = groupId;
    }

    @Override
    public Object execute(CommandContext commandContext) {
        if (userId == null) {
            throw new FlowableIllegalArgumentException("userId is null");
        }
        if (groupId == null) {
            throw new FlowableIllegalArgumentException("groupId is null");
        }
        CommandContextUtil.getMembershipEntityManager(commandContext).createMembership(userId, groupId);
        return null;
    }
}

View on GitHub (pinned to d6d39ce1c6)

Solutions

  1. Pass a non-null userId that references an existing user.
  2. Create the user first (identityService.newUser/saveUser) before creating the membership.
  3. Validate both ids before calling createMembership.

Example fix

// before
identityService.createMembership(user.getId(), group.getId()); // user.getId() null
// after
if (user.getId() != null) {
    identityService.createMembership(user.getId(), group.getId());
} else {
    identityService.saveUser(user); // persist to obtain the id first
    identityService.createMembership(user.getId(), group.getId());
}
Defensive patterns

Strategy: validation

Validate before calling

if (userId != null && groupId != null) { identityService.createMembership(userId, groupId); }

Type guard

boolean canCreateMembership(String userId, String groupId) { return userId != null && groupId != null; }

Try / catch

try { identityService.createMembership(userId, groupId); } catch (FlowableIllegalArgumentException e) { log.error("Membership needs non-null userId and groupId", e); }

Prevention

When it happens

Trigger: Calling identityService.createMembership(null, groupId) — the command executes and fails its userId check.

Common situations: Bulk user/group synchronization jobs where a user record failed to load or the id field is null in the source data.

Related errors

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/f052a28da9e57e8a. Report an issue: GitHub.