code: public static Thread findThreadById(final long threadId) {
          final Collection<Thread> result = findThreads(new ThreadIdPredicate(threadId));
          return result.isEmpty() ? null : result.iterator().next();
      }
docs: Return the active thread with the specified id.
  
  @param threadId The thread id
  @return The thread with the specified id or {@code null} if no such thread exists
  @throws IllegalArgumentException if the specified id is zero or negative
  @throws  SecurityException
  if the current thread cannot access the system thread group
  
  @throws  SecurityException  if the current thread cannot modify
  thread groups from this thread's thread group up to the system thread group