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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,/**.template.dart}> File paths in Glob syntax to be exclude.
(defaults to "{/**.g.dart,/**.template.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