code: public static void assertNotNullEightBytes(byte[] bytes) {
          if (bytes == null) {
              throw new IllegalArgumentException("Expected 8 bytes, but got null.");
          }
          if (bytes.length != 8) {
              throw new IllegalArgumentException(String.format("Expected 8 bytes, but got: %d bytes.", bytes.length));
          }
      }
docs: Thrown an {@link IllegalArgumentException} when the byte array does not contain exactly eight bytes.
  
  @param bytes Byte array.