code: public static ByteBuf threadLocalDirectBuffer() {
          if (THREAD_LOCAL_BUFFER_SIZE <= 0) {
              return null;
          }
  
          if (PlatformDependent.hasUnsafe()) {
              return ThreadLocalUnsafeDirectByteBuf.newInstance();
          } else {
              return ThreadLocalDirectByteBuf.newInstance();
          }
      }
docs: Returns a cached thread-local direct buffer, if available.
  
  @return a cached thread-local direct buffer, if available.  {@code null} otherwise.