docs: public static ClassLoader getAndSetLoader(ClassLoader newCL) {
          ThreadContextAccessor tca = ThreadContextAccessor.getThreadContextAccessor();
          //This could be a ClassLoader or the special type UNCHANGED.
          Object maybeOldCL = tca.pushContextClassLoaderForUnprivileged(newCL);
          if (maybeOldCL instanceof ClassLoader) {
              return (ClassLoader) maybeOldCL;
          } else {
              return newCL;
          }
      }