DOMDocument->getDocumentElement() returns NULL without any exception

I have parsed a special file encoded in ISO-8859 (command file) where its spaces are special characters (not the classical space character).

When parsing, there is no error, no exception, no warning. But DOMDocument->getDocumentElement() returns the NULL value (this case is not mentionned in the the documentation).

Here is a dump of the file :
00000000 3c 6e 6f 64 65 3e 0a a0 a0 a0 3c 70 72 6f 70 65 |<node>.   <prope|
00000010 72 74 69 65 73 3e 0a a0 a0 3c 2f 70 72 6f 70 65 |rties>.  </prope|
00000020 72 74 69 65 73 3e 0a 3c 2f 6e 6f 64 65 3e 0a 0a |rties>.</node>..|
00000030 0a 3c 21 2d 2d 20 65 6f 66 20 2d 2d 3e 0a |.<!-- eof -->.|
0000003e