Skip to main content

Check unnecessary nullable parameters

Checks unnecessary nullable parameters in functions, methods, constructors. Removing unnecessary nullables can help reduce amount of checks in the code.

To execute the command, run

$ dart run dart_code_metrics:metrics check-unnecessary-nullable lib

# or for a Flutter package
$ flutter pub run dart_code_metrics:metrics check-unnecessary-nullable lib

Full command description:

Usage: metrics check-unnecessary-nullable [arguments] <directories>
-h, --help Print this usage information.

-r, --reporter=<console> The format of the output of the analysis.
[console (default), json]

-c, --print-config Print resolved config.

--root-folder=<./> Root folder.
(defaults to current directory)
--sdk-path=<directory-path> Dart SDK directory path. Should be provided only when you run the application as compiled executable( and automatic Dart SDK path detection fails.
--exclude=<{/**.g.dart,/**.freezed.dart}> File paths in Glob syntax to be exclude.
(defaults to "{/**.g.dart,/**.freezed.dart}")

--no-congratulate Don't show output even when there are no issues.

--[no-]monorepo Treat all exported code with parameters as non-nullable by default.

--[no-]fatal-found Treat found unnecessary nullable parameters as fatal.

Suppressing the command

In order to suppress the command add the ignore: unnecessary-nullable comment. To suppress for an entire file add ignore_for_file: unnecessary-nullable to the beginning of a file.

Monorepo support

By default the command treats all code that is exported from the package as used. To disable this behavior use --monorepo flag. This might be useful when all the packages in your repository are only used within the repository and are not published to the pub.

Output example


Use --reporter=console to enable this format.



The reporter prints a single JSON object containing meta information and the unnecessary nullable parameters. Use --reporter=json to enable this format.

The root object fields are

  • formatVersion - an integer representing the format version (will be incremented each time the serialization format changes)
  • timestamp - a creation time of the report in YYYY-MM-DD HH:MM:SS format
  • unnecessaryNullable - an array of unnecessary nullable issues
"formatVersion": 2,
"timestamp": "2021-04-11 14:44:42",
"unnecessaryNullable": [

The unnecessaryNullable object fields are

  • path - a relative path of the file with unnecessary nullable parameters declaration
  • issues - an array of issues detected in the target class
"path": "lib/src/some/class.dart",
"issues": [

The issue object fields are

  • declarationName - the name of a declaration with unnecessary nullable parameters
  • declarationType - the type of a declaration with unnecessary nullable parameters (function, method or constructor)
  • parameters - an array of strings representing parameters that are marked as nullable
  • offset - a zero-based offset of the class member location in the source
  • line - a zero-based line of the class member location in the source
  • column - a zero-based column of class member the location in the source
"declarationName": "someFunction",
"declarationType": "function",
"parameters": "[String? value]",
"offset": 156,
"line": 7,
"column": 1