statix linting - Githubissues

After running niv init, statix check has a few suggestions for nix/sources.nix:
$ statix check
[bin/src/config.rs:79] [self.ignore.as_slice(), extra_ignores].concat() = []
[W19] Warning: This `if` expression can be simplified with `or`
    ╭─[./nix/sources.nix:38:7]
    │
 38 │ ╭─▶       if spec ? ref
 44 │ ├─▶       else abort "In git source '${name}': Please specify `ref`, `tag` or `branch`!";
    · │                                                                                           
    · ╰─────────────────────────────────────────────────────────────────────────────────────────── Consider using spec.ref or (if spec ? branch
      then "refs/heads/${spec.branch}"
      else if spec ? tag
      then "refs/tags/${spec.tag}"
      else abort "In git source '${name}': Please specify ref, tag or branch!") instead of this if expression
────╯
[W19] Warning: This `if` expression can be simplified with `or`
    ╭─[./nix/sources.nix:46:7]
    │
 46 │ ╭─▶       if spec ? submodules
 48 │ ├─▶       else false;
    · │                       
    · ╰─────────────────────── Consider using spec.submodules or false instead of this if expression
────╯
[W01] Warning: Unnecessary comparison with boolean
    ╭─[./nix/sources.nix:52:12]
    │
 52 │         if submodules == true
    ·            ─────────┬────────  
    ·                     ╰────────── Comparing submodules with boolean literal true
────╯
[W13] Warning: Found usage of deprecated builtin isNull
     ╭─[./nix/sources.nix:143:10]
     │
 143 │       if isNull (builtins.match "[a-zA-Z0-9]" c)
     ·          ───────────────────┬───────────────────  
     ·                             ╰───────────────────── isNull is deprecated, check equality with null instead
─────╯
[W13] Warning: Found usage of deprecated builtin isNull
     ╭─[./nix/sources.nix:201:59]
     │
 201 │     then fetchTarball ({inherit url;} // (optionalAttrs (!isNull name) {inherit name;}))
     ·                                                           ─────┬─────  
     ·                                                                ╰─────── isNull is deprecated, check equality with null instead
─────╯
[W13] Warning: Found usage of deprecated builtin isNull
     ╭─[./nix/sources.nix:213:55]
     │
 213 │     then fetchurl ({inherit url;} // (optionalAttrs (!isNull name) {inherit name;}))
     ·                                                       ─────┬─────  
     ·                                                            ╰─────── isNull is deprecated, check equality with null instead
─────╯
[W13] Warning: Found usage of deprecated builtin isNull
     ╭─[./nix/sources.nix:235:10]
     │
 235 │       if isNull sourcesFile
     ·          ─────────┬────────  
     ·                   ╰────────── isNull is deprecated, check equality with null instead
─────╯
There might be excellent reasons for these (such as backwards compatibility), but since I couldn't find them in the issue tracker I thought they would be worth mentioning.
nmattia / niv

statix linting #362
