Merge branch 'feature/REQ-5965' into test

workflow-engine-core/src/main/java/cn/axzo/workflow/core/engine/cmd/CustomApproveTaskCmd.java

@@ -210,6 +210,9 @@ public class CustomApproveTaskCmd extends AbstractCommand<Void> implements Seria
                                        List<AttachmentDTO> attachmentList,
                                        String advice,
                                        BpmnTaskDelegateAssigner approver) {
+        if (Objects.isNull(approver)) {
+            return;
+        }
         List<SignatureDTO> signatures = runtimeService.getVariable(task.getProcessInstanceId(), SIGNATURE_COLLECTION, List.class);
         if (Objects.isNull(signatures)) {
             signatures = new ArrayList<>();