public ByteVector putByteArray(final byte[] b, final int off, final int len) {
		if (length + len > data.length) {
			enlarge(len);
		}
		if (b != null) {
			System.arraycopy(b, off, data, length, len);
		}
		length += len;
		return this;
	}
Puts an array of bytes into this byte vector. The byte vector is
automatically enlarged if necessary.

@param b   an array of bytes. May be <tt>null</tt> to put <tt>len</tt> null
           bytes into this byte vector.
@param off index of the fist byte of b that must be copied.
@param len number of bytes of b that must be copied.
@return this byte vector.
src/main/java/com/alibaba/fastjson/asm/ByteVector.java