MDL-21146 $CFG can not be used in low level file operations - please set the defaults...

MDL-21146 $CFG can not be used in low level file operations - please set the defaults elsewhere if really necessary; removing the extra cleaning + undefined notices - please make sure all palces that actually output the strings are processed properly, there is no way around this, cleaning must be always done before output, not just storage; using real nulls where we do not know the value