DateTime::createFromFormat handles NULL args
DateTime::createFromFormat handles NULL args

fixes https://github.com/peachpiecompiler/peachpie/issues/820

peachpiecompiler/peachpie,iolevel/peachpie-concept,peachpiecompiler/peachpie,peachpiecompiler/peachpie,iolevel/peachpie-concept,iolevel/peachpie-concept