@Override
    public void write(FieldBase field, PredicateFieldValue value) {
        byte[] buf = BinaryFormat.encode(value.getPredicate());
        this.buf.putInt(buf.length);
        this.buf.put(buf);
    }
Write out the value of raw field

@param field - field description (name and data type)
@param value - field value
document/src/main/java/com/yahoo/document/serialization/VespaDocumentSerializer6.java