Return value changed in 5.3.3 - between 5.3.0 and 5.3.2 (incl.) when the result set was empty NULL was returned. 5.3.3+ returns an empty array.
Also, mysqli_fetch_all works only for buffered result sets, which are the default for mysqli_query. MYSQLI_USE_RESULT will be supported in 5.3.4+
However, it makes little sense to use it this way, materialising unbuffered sets. In this case choose STORE_RESULT, and fetch_all won't copy the data, but reference it, as it is stored already in mysqlnd.