docs: @Trivial
      protected SubjectThreadContext getSubjectThreadContext() {
          ThreadLocal<SubjectThreadContext> currentThreadLocal = getThreadLocal();
          SubjectThreadContext subjectThreadContext = currentThreadLocal.get();
          if (subjectThreadContext == null) {
              subjectThreadContext = new SubjectThreadContext();
              currentThreadLocal.set(subjectThreadContext);
          }
          return subjectThreadContext;
      }