Revert 981cc42 allow null in getDirectoryContents
Revert 981cc42 allow null in getDirectoryContents

Revert 981cc42 allowing null parameter in
`Environment::getDirectoryContents()` as type juggling of interface
feels like it will encourage bad habits that cannot be taken back later.

Commit 1ffe834680d056b1cabe66b42cdd67d41254a50f [formerly 981cc429e282a379e8b4930cbc8fffaf89f07752]


Former-commit-id: 60c7b535a46036621b77c0edeb0d2c6fde2dded8
rikzuiderlicht/concrete5,triplei/concrete5-8,olsgreen/concrete5,KorvinSzanto/concrete5,a3020/concrete5,deek87/concrete5,acliss19xx/concrete5,mlocati/concrete5,olsgreen/concrete5,deek87/concrete5,acliss19xx/concrete5,a3020/concrete5,biplobice/concrete5,hissy/concrete5,KorvinSzanto/concrete5,acliss19xx/concrete5,triplei/concrete5-8,rikzuiderlicht/concrete5,olsgreen/concrete5,deek87/concrete5,MrKarlDilkington/concrete5,triplei/concrete5-8,concrete5/concrete5,jaromirdalecky/concrete5,MrKarlDilkington/concrete5,hissy/concrete5,biplobice/concrete5,haeflimi/concrete5,haeflimi/concrete5,hissy/concrete5,mlocati/concrete5,mainio/concrete5,concrete5/concrete5,mainio/concrete5,hissy/concrete5,deek87/concrete5,mlocati/concrete5,mainio/concrete5,haeflimi/concrete5,MrKarlDilkington/concrete5,haeflimi/concrete5,mlocati/concrete5,KorvinSzanto/concrete5,rikzuiderlicht/concrete5,jaromirdalecky/concrete5,biplobice/concrete5,jaromirdalecky/concrete5,jaromirdalecky/concrete5,biplobice/concrete5,concrete5/concrete5,concrete5/concrete5