In my case,
INSERT INTO xmltable (id, xml_content)
VALUES (?,XMLPARSE(DOCUMENT '<?xml version=\"1.0\" encoding=\"UTF-8\"?><mail><from>abc</from><to>xyz</to></mail>' PRESERVE WHITESPACE))
is working fine, but
INSERT INTO xmltable (id, xml_content)
VALUES (?,XMLPARSE(DOCUMENT ? PRESERVE WHITESPACE))
is not.