>This is correct behavior. \x00 is not supported in XML:
> not in raw form, and not in escaped form

last sentence in forth paragraph of section 1.3 in XML 1.1 specification says following:
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Due to potential problems with APIs,
#x0 is still forbidden both directly and as a character reference.
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And, second sentence in paragraph 2 in subsection 'Validity constraint: Notation Declared' of section 4.2.2 says following:
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The characters to be escaped are the control characters #x0 to #x1F and #x7F (most of which cannot appear in XML), space #x20, the delimiters '<' #x3C, '>' #x3E and '"' #x22, the unwise characters '{' #x7B, '}' #x7D, '|' #x7C, '\' #x5C, '^' #x5E and '`' #x60, as well as all characters above #x7F.
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(xml 1.1) http://www.w3.org/TR/2006/REC-xml11-20060816/
(xml 1.0) http://www.w3.org/TR/2008/REC-xml-20081126/