[TASK] Prevent fatal Exceptions for removed FAL references
[TASK] Display friendly but grave error when file field value nullified
Merge pull request #119 from NamelessCoder/removedfiles

[TASK] Prevent fatal Exceptions for removed FAL references
[TASK] Code style cleanups phase 1: Code smells
[TASK] Code style cleanups phase 2: Code style
[TASK] Code style cleanups phase 3: Doc comment consistency
[TASK] Code style cleanups phase 4: Parameter- and return types
[BUGFIX] Code style cleanups phase 5: References to missing variables
[BUGFIX] Code style cleanups phase 6: Undefined variables
[BUGFIX] Code style cleanups phase 7: Undefined and unused variables
[BUGFIX] Unintentional nullification of FlexForm ID