JAVA.NULL.RET.NONNULL : Method Should Not Return null (Java)

要旨

A method returns null but is normally assumed to return a non-null value.

If null is dereferenced, Java runs into a NullPointerException. For this reason, programmers must ensure that the content of expressions dereferenced in their programs is never null.

CodeSonar provides two sets of warning classes covering various aspects of null value handling.

• The JAVA.NULL.* classes involve faster checks over a more limited set of circumstances, and issue a more restricted set of false positive warnings. These are often the best way to rapidly identify the most frequent null pointer errors in a program.
• The JAVA.DEEPNULL.* classes involve deeper checking over all possible situations. These checks tend to take longer than the JAVA.NULL.* checks and have more false positives.

For the most comprehensive null pointer checking, enable both sets of warning classes: JAVA.NULL.* and JAVA.DEEPNULL.*

Strict and Non-Strict Checking

When JAVA_ANALYSIS_STRICT_MODE=No, warnings of this class will not be issued if there are indications that the possibility of a NullPointerException has been recognized and accounted for. For example, warnings will not be issued for code inside a try-catch block that explicitly catches NullPointerException, or for a JUnit test that is annotated as expecting this exception.

When JAVA_ANALYSIS_STRICT_MODE=Yes, warnings will be issued even in these cases.

プロパティ

WARNING_FILTER += discard class="Method Should Not Return null (Java)"

例

public class ConventionExample {

    public static void main(String[] args) {
        MyClass cs = new MyClass();
        String s = cs.toString();
    }
    
    public static class MyClass {
        @Override
        public String toString() {
            return null; // "Method Should Not Return null (Java)" warning issued here 
        }
    }
}

解決法

Check if the warning corresponds to a situation where null might actually be dereferenced at runtime. If that is the case, add a nullness check for the value being dereferenced, or change the logic of the code. Sometimes, a warning of this checker corresponds to a spurious nullness check, that can be removed.

関連のある設定ファイルパラメータ

設定ファイルの以下のパラメータがこのワーニングクラスのチェックに影響します。

• JAVA_ANALYSIS_STRICT_MODE
• REPORT_SIMILAR_WARNINGS
• WARNING_FILTER