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copied!<p>Your implementation is wrong ;)</p> <p>Basically docs says (I'll paraphrase and emphasise):</p> <blockquote> <p><code>@throws NullPointerException</code> if <code>input</code> is null and <strong>the concrete function implementation</strong> does not accept null arguments</p> </blockquote> <p>By implementing your function you must decide if it accepts nulls or not. In first case:</p> <pre><code>private static final class Example implements Function<MyBean, String> { @Override @Nullable public String apply(@Nullable MyBean input) { return input == null ? null : input.field; } } </code></pre> <p>In second case:</p> <pre><code>private static final class Example implements Function<MyBean, String> { @Override @Nullable public String apply(MyBean input) { if (null == input) { throw new NullPointerException(); } return input.field; } } </code></pre> <p>In both examples returning null is allowed.</p> <p><strong>EDIT:</strong></p> <p>Note that Guava uses <code>@javax.annotation.ParametersAreNonnullByDefault</code> on all packages, hence if <code>@Nullable</code> is present it means "suspend global <code>@Nonnull</code> and allow nulls here" and if not it means "nulls forbidden here". </p> <p>That said, you may want use <code>@Nonnull</code> annotation on your argument or <code>@ParametersAreNonnullByDefault</code> in package to tell FindBugs Function's argument can't be null.</p> <p><strong>EDIT 2:</strong></p> <p>Turns out <a href="http://code.google.com/p/guava-libraries/issues/detail?id=920" rel="noreferrer">this case is known issue</a>, see comment #3 (from Guava's lead dev Kevin Bourrillion, about his conversation with Bill Pugh, Findbugs' lead):</p> <blockquote> <p>My reference was a series of in-person conversations with Bill Pugh. He asserted unambiguously that <code>@Nullable</code> means only that some subtypes <em>might</em> accept null. And this seems to be borne out by findbugs for us -- our code passes the nullability checks pretty cleanly (though we should check again since this particular Function change was made).</p> </blockquote>

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