{"id":15039149,"url":"https://github.com/uber/nullaway","last_synced_at":"2025-05-13T16:09:54.783Z","repository":{"id":37269808,"uuid":"102137661","full_name":"uber/NullAway","owner":"uber","description":"A tool to help eliminate NullPointerExceptions (NPEs) in your Java code with low build-time overhead","archived":false,"fork":false,"pushed_at":"2025-04-16T03:41:01.000Z","size":6949,"stargazers_count":3721,"open_issues_count":119,"forks_count":302,"subscribers_count":70,"default_branch":"master","last_synced_at":"2025-04-16T04:46:04.931Z","etag":null,"topics":["android","java","nullability","nullability-analysis","static-analysis","static-code-analysis"],"latest_commit_sha":null,"homepage":"","language":"Java","has_issues":true,"has_wiki":null,"has_pages":null,"mirror_url":null,"source_name":null,"license":"mit","status":null,"scm":"git","pull_requests_enabled":true,"icon_url":"https://github.com/uber.png","metadata":{"files":{"readme":"README.md","changelog":"CHANGELOG.md","contributing":"CONTRIBUTING.md","funding":null,"license":"LICENSE.txt","code_of_conduct":"CODE_OF_CONDUCT.md","threat_model":null,"audit":null,"citation":null,"codeowners":null,"security":null,"support":null,"governance":null,"roadmap":null,"authors":null,"dei":null,"publiccode":null,"codemeta":null,"zenodo":null}},"created_at":"2017-09-01T17:35:57.000Z","updated_at":"2025-04-14T22:36:23.000Z","dependencies_parsed_at":"2023-09-28T18:30:24.096Z","dependency_job_id":"dcb17a8a-5842-445a-87fa-c786a22355ed","html_url":"https://github.com/uber/NullAway","commit_stats":null,"previous_names":[],"tags_count":103,"template":false,"template_full_name":null,"repository_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/uber%2FNullAway","tags_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/uber%2FNullAway/tags","releases_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/uber%2FNullAway/releases","manifests_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/uber%2FNullAway/manifests","owner_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners/uber","download_url":"https://codeload.github.com/uber/NullAway/tar.gz/refs/heads/master","host":{"name":"GitHub","url":"https://github.com","kind":"github","repositories_count":250514762,"owners_count":21443208,"icon_url":"https://github.com/github.png","version":null,"created_at":"2022-05-30T11:31:42.601Z","updated_at":"2022-07-04T15:15:14.044Z","host_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub","repositories_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories","repository_names_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repository_names","owners_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners"}},"keywords":["android","java","nullability","nullability-analysis","static-analysis","static-code-analysis"],"created_at":"2024-09-24T20:41:45.494Z","updated_at":"2025-04-23T20:53:04.782Z","avatar_url":"https://github.com/uber.png","language":"Java","readme":"## NullAway: Fast Annotation-Based Null Checking for Java [![Build Status](https://github.com/uber/nullaway/actions/workflows/continuous-integration.yml/badge.svg)](https://github.com/uber/nullaway/actions/workflows/continuous-integration.yml) [![Coverage Status](https://codecov.io/github/uber/NullAway/coverage.svg?branch=master)](https://codecov.io/github/uber/NullAway?branch=master)\n\nNullAway is a tool to help eliminate `NullPointerException`s (NPEs) in your Java code.  To use NullAway, first add `@Nullable` annotations in your code wherever a field, method parameter, or return value may be `null`.  Given these annotations, NullAway performs a series of type-based, local checks to ensure that any pointer that gets dereferenced in your code cannot be `null`.  NullAway is similar to the type-based nullability checking in the Kotlin and Swift languages, and the [Checker Framework](https://checkerframework.org/) and [Eradicate](https://fbinfer.com/docs/checker-eradicate/) null checkers for Java.\n\nNullAway is *fast*.  It is built as a plugin to [Error Prone](http://errorprone.info/) and can run on every single build of your code.  In our measurements, the build-time overhead of running NullAway is usually less than 10%.  NullAway is also *practical*: it does not prevent all possible NPEs in your code, but it catches most of the NPEs we have observed in production while imposing a reasonable annotation burden, giving a great \"bang for your buck.\"\n\n## Installation\n\n### Overview\n\nNullAway requires that you build your code with [Error Prone](http://errorprone.info), version 2.14.0 or higher.  See the [Error Prone documentation](http://errorprone.info/docs/installation) for instructions on getting started with Error Prone and integration with your build system.  The instructions below assume you are using Gradle; see [the docs](https://github.com/uber/NullAway/wiki/Configuration#other-build-systems) for discussion of other build systems.\n\n### Gradle\n\n#### Java (non-Android)\n\nTo integrate NullAway into your non-Android Java project, add the following to your `build.gradle` file:\n\n```gradle\nplugins {\n  // we assume you are already using the Java plugin\n  id \"net.ltgt.errorprone\" version \"\u003cplugin version\u003e\"\n}\n\ndependencies {\n  errorprone \"com.uber.nullaway:nullaway:\u003cNullAway version\u003e\"\n\n  // Some source of nullability annotations; JSpecify recommended,\n  // but others supported as well.\n  api \"org.jspecify:jspecify:1.0.0\"\n\n  errorprone \"com.google.errorprone:error_prone_core:\u003cError Prone version\u003e\"\n}\n\nimport net.ltgt.gradle.errorprone.CheckSeverity\n\ntasks.withType(JavaCompile) {\n  options.errorprone {\n    check(\"NullAway\", CheckSeverity.ERROR)\n    option(\"NullAway:AnnotatedPackages\", \"com.uber\")\n  }\n  // Include to disable NullAway on test code\n  if (name.toLowerCase().contains(\"test\")) {\n    options.errorprone {\n      disable(\"NullAway\")\n    }\n  }\n}\n```\n\nLet's walk through this script step by step.  The `plugins` section pulls in the [Gradle Error Prone plugin](https://github.com/tbroyer/gradle-errorprone-plugin) for Error Prone integration.\n\nIn `dependencies`, the first `errorprone` line loads NullAway, and the `api` line loads the [JSpecify](https://jspecify.dev) library which provides suitable nullability annotations, e.g., `org.jspecify.annotations.Nullable`.  NullAway allows for any `@Nullable` annotation to be used, so, e.g., `@Nullable` from the AndroidX annotations Library or JetBrains annotations is also fine. The second `errorprone` line sets the version of Error Prone is used.\n\nFinally, in the `tasks.withType(JavaCompile)` section, we pass some configuration options to NullAway.  First `check(\"NullAway\", CheckSeverity.ERROR)` sets NullAway issues to the error level (it's equivalent to the `-Xep:NullAway:ERROR` standard Error Prone argument); by default NullAway emits warnings.  Then, `option(\"NullAway:AnnotatedPackages\", \"com.uber\")` (equivalent to the `-XepOpt:NullAway:AnnotatedPackages=com.uber` standard Error Prone argument) tells NullAway that source code in packages under the `com.uber` namespace should be checked for null dereferences and proper usage of `@Nullable` annotations, and that class files in these packages should be assumed to have correct usage of `@Nullable` (see [the docs](https://github.com/uber/NullAway/wiki/Configuration) for more detail).  NullAway requires exactly one of the `AnnotatedPackages` or `OnlyNullMarked` configuration arguments to run, in order to distinguish between annotated and unannotated code.  See [the configuration docs](https://github.com/uber/NullAway/wiki/Configuration) for more details and other useful configuration options.  For even simpler configuration of NullAway options, use the [Gradle NullAway plugin](https://github.com/tbroyer/gradle-nullaway-plugin).  Finally, we show how to disable NullAway on test code, if desired.\n\nWe recommend addressing all the issues that Error Prone reports, particularly those reported as errors (rather than warnings).  But, if you'd like to try out NullAway without running other Error Prone checks, you can use `options.errorprone.disableAllChecks` (equivalent to passing `\"-XepDisableAllChecks\"` to the compiler, before the NullAway-specific arguments).\n\n#### Android\n\nVersions 3.0.0 and later of the Gradle Error Prone Plugin [no longer support Android](https://github.com/tbroyer/gradle-errorprone-plugin/releases/tag/v3.0.0).  So if you're using a recent version of this plugin, you'll need to add some further configuration to run Error Prone and NullAway.  Our [sample app `build.gradle` file](https://github.com/uber/NullAway/blob/master/sample-app/build.gradle) shows one way to do this, but your Android project may require tweaks.  Alternately, 2.x versions of the Gradle Error Prone Plugin still support Android and may still work with your project.\n\nBeyond that, compared to the Java configuration, the JSpecify dependency can be removed; you can use the `androidx.annotation.Nullable` annotation from the AndroidX annotation library instead.\n\n#### Annotation Processors / Generated Code\n\nSome annotation processors like [Dagger](https://google.github.io/dagger/) and [AutoValue](https://github.com/google/auto/tree/master/value) generate code into the same package namespace as your own code.  This can cause problems when setting NullAway to the `ERROR` level as suggested above, since errors in this generated code will block the build.  Currently the best solution to this problem is to completely disable Error Prone on generated code, using the `-XepExcludedPaths` option added in Error Prone 2.1.3 (documented [here](http://errorprone.info/docs/flags), use `options.errorprone.excludedPaths=` in Gradle).  To use, figure out which directory contains the generated code, and add that directory to the excluded path regex.\n\n**Note for Dagger users**: Dagger versions older than 2.12 can have bad interactions with NullAway; see [here](https://github.com/uber/NullAway/issues/48#issuecomment-340018409).  Please update to Dagger 2.12 to fix the problem.\n\n#### Lombok\n\nUnlike other annotation processors above, Lombok modifies the in-memory AST of the code it processes, which is the source of numerous incompatibilities with Error Prone and, consequently, NullAway. \n\nWe do not particularly recommend using NullAway with Lombok. However, NullAway encodes some knowledge of common Lombok annotations and we do try for best-effort compatibility. In particular, common usages like `@lombok.Builder` and `@Data` classes should be supported.\n\nIn order for NullAway to successfully detect Lombok generated code within the in-memory Java AST, the following configuration option must be passed to Lombok as part of an applicable `lombok.config` file:\n\n```\nlombok.addLombokGeneratedAnnotation = true\n```\n\nThis causes Lombok to add `@lombok.Generated` to the methods/classes it generates. NullAway will ignore (i.e. not check) the implementation of this generated code, treating it as unannotated. \n\n## Code Example\n\nLet's see how NullAway works on a simple code example:\n```java\nstatic void log(Object x) {\n    System.out.println(x.toString());\n}\nstatic void foo() {\n    log(null);\n}\n```\nThis code is buggy: when `foo()` is called, the subsequent call to `log()` will fail with an NPE.  You can see this error in the NullAway sample app by running:\n```bash\ncp sample/src/main/java/com/uber/mylib/MyClass.java.buggy sample/src/main/java/com/uber/mylib/MyClass.java\n./gradlew build\n```\n\nBy default, NullAway assumes every method parameter, return value, and field is _non-null_, i.e., it can never be assigned a `null` value.  In the above code, the `x` parameter of `log()` is assumed to be non-null.  So, NullAway reports the following error:\n```\nwarning: [NullAway] passing @Nullable parameter 'null' where @NonNull is required\n    log(null);\n        ^\n```\nWe can fix this error by allowing `null` to be passed to `log()`, with a `@Nullable` annotation:\n```java\nstatic void log(@Nullable Object x) {\n    System.out.println(x.toString());\n}\n```\nWith this annotation, NullAway points out the possible null dereference:\n```\nwarning: [NullAway] dereferenced expression x is @Nullable\n    System.out.println(x.toString());\n                        ^\n```\nWe can fix this warning by adding a null check:\n```java\nstatic void log(@Nullable Object x) {\n    if (x != null) {\n        System.out.println(x.toString());\n    }\n}\n```\nWith this change, all the NullAway warnings are fixed.\n\nFor more details on NullAway's checks, error messages, and limitations, see [our detailed guide](https://github.com/uber/NullAway/wiki).\n\n## Support\n\nPlease feel free to [open a GitHub issue](https://github.com/uber/NullAway/issues) if you have any questions on how to use NullAway.  Or, you can [join the NullAway Discord server](https://discord.gg/QH2F779) and ask us a question there.\n\n## Contributors\n\nWe'd love for you to contribute to NullAway!  Please note that once\nyou create a pull request, you will be asked to sign our [Uber Contributor License Agreement](https://docs.google.com/a/uber.com/forms/d/1pAwS_-dA1KhPlfxzYLBqK6rsSWwRwH95OCCZrcsY5rk/viewform).\n\n## License\n\nNullAway is licensed under the MIT license.  See the LICENSE.txt file for more information.\n","funding_links":[],"categories":[],"sub_categories":[],"project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fuber%2Fnullaway","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fuber%2Fnullaway","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fuber%2Fnullaway/lists"}