question: public byte [ ] toByteArray ( ) { if ( headerNonce_ == null || headerTag_ == null ) { throw new AwsCryptoException ( "Header nonce and tag cannot be null." ) ; } final byte [ ] serializedFields = serializeAuthenticatedFields ( ) ; final int outLen = serializedFields . length + headerNonce_ . length + headerTag_ . length ; final ByteBuffer serializedBytes = ByteBuffer . allocate ( outLen ) ; serializedBytes . put ( serializedFields ) ; serializedBytes . put ( headerNonce_ ) ; serializedBytes . put ( headerTag_ ) ; return serializedBytes . array ( ) ; }
target:  Serialize the header fields into a byte array. This method serializes all the header fields including the header nonce and tag.