readChunk() {

		if ( this.endOfChunk ) {

			return null;

		}

		try {

			const next = new Chunk( this.data, this.position, this.debugMessage );
			this.position += next.size;
			return next;

		}	catch ( e ) {

			this.debugMessage( 'Unable to read chunk at ' + this.position );
			return null;

		}

	}
Reads a sub cchunk.

@private
@return {Chunk | null} next sub chunk.