Problem:    Crash when using null_class.
Solution:   Give an error when trying to use a null class.

Problem:    Condition is always true.
Solution:   Remove the condition. (closes #12139)

Problem:    find_file_in_path() is not reentrant.
Solution:   Instead of global variables pass pointers to the functions.
            (closes #12093)

Problem:    Highlight test script has a few problems.
Solution:   Rewrite the script in Vim9 syntax. (closes #10379)

Problem:    Profile test repeats the headers many times.
Solution:   Put the headers in script variables.

Problem:    Highlight for popupmenu kind and extra cannot be set.
Solution:   Add PmenuKind, PmenuKindSel, PmenuExtra and PmenuExtraSel
            highlight groups and use them. (Gianmaria Bajo, closes #12114)

Problem:    sort(list, 'N') does not work in Vim9 script context.
Solution:   Convert string to number without giving an error. (closes #12061)

Problem:    Odin files are not recognized.
Solution:   Add a pattern for Odin files. (Amaan Qureshi, closes #12122)

Problem:    Unx Tal files are not recognized.
Solution:   Add a pattern for Unx Tal files. (Amaan Qureshi, closes #12117)

Problem:    Cairo files are not recognized.
Solution:   Add a pattern for Cairo files. (Amaan Qureshi, closes #12118)