Xembly does not allow this:
```
java.lang.IllegalArgumentException: org.xembly.XmlContentException: Character #00 is in restricted XML range #00-#08, see http://www.w3.org/TR/2004/REC-xml11-20040204/#charsets
	at org.xembly.Directives.set(Directives.java:295)
	at com.jcabi.github.mock.MkContents.create(MkContents.java:121)
	at com.jcabi.github.mock.MkContentTest.fetchesRawRepresentation(MkContentTest.java:115)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
...
```