AssignmentToNull

Reports variables that are assigned to null outside a declaration.

The main purpose of null in Java is to denote uninitialized reference variables. In rare cases, assigning a variable explicitly to null is useful to aid garbage collection. However, using null to denote a missing, not specified, or invalid value or a not found element is considered bad practice and may make your code more prone to NullPointerExceptions. Instead, consider defining a sentinel object with the intended semantics or use library types like Optional to denote the absence of a value.

Example:

Integer convert(String s) {
    Integer value;
    try {
      value = Integer.parseInt(s);
    } catch (NumberFormatException e) {
      // Warning: null is used to denote an 'invalid value'
      value = null;
    }
    return value;
  }

Use the Ignore assignments to fields option to ignore assignments to fields.