java Sonar issue参数必须为非Null，但标记为可为Null

Question

我写了这个谓词，sonar对此表示不满。我不知道如何纠正这一违规行为。请帮助：

import com.google.common.base.Predicate;

import java.util.Map;
public final class FooPredicate {

    private FooPredicate(){}

    public static Predicate<Map.Entry<Long,Long>> isFirstElement(final Long o) {
        return new Predicate<Map.Entry<Long,Long>>() {
            @Override
            public boolean apply(Map.Entry<Long,Long> foo) { 
                return foo.getKey().equals(o);
            }
        };
    }
}

它向apply方法抱怨Foo参数

Dodgy - Parameter must be nonnull but is marked as nullable
foo must be nonnull but is marked as nullable

apply方法被定义为接受一个null值，对此我无能为力。声纳和番石榴不是在这里战斗吗

> boolean apply(@Nullable
>             T input)
> 
> Returns the result of applying this predicate to input. This method is
> generally expected, but not absolutely required, to have the following
> properties:
> 
>     Its execution does not cause any observable side effects.
>     The computation is consistent with equals; that is, Objects.equal(a, b) implies that predicate.apply(a) ==
> predicate.apply(b)). 
> 
> Throws:
>     NullPointerException - if input is null and this predicate does not accept null arguments

Answer 1

你正在做foo.getKey()。如果foo为null，则将引发NullPointerException，但您没有声明foo不能为null

在使用前检查空值foo

if (foo != null) {
   return foo.getKey().equals(o);
} else {
   return null;
}