title: Spring nullable annotation generates unknown enum constant warning
body: <p>In my app, whenever I add <code>@Nullable</code> (which imports from <code>org.springframework.lang.Nullable</code>) to any of the fields, I get a build warning: </p>
  
  <blockquote>
    <p>Warning:java: unknown enum constant javax.annotation.meta.When.MAYBE
      reason: class file for javax.annotation.meta.When not found</p>
  </blockquote>
  
  <p><code>@NonNull</code> and other null safety annoations from spring compile without any warnings as its implementation doesn't import <code>import javax.annotation.meta.When</code>. </p>
  
  <p>The application runs just fine but the warning is just annoying. I am using spring boot <code>2.1.0</code> and java version <code>1.8.0_191</code></p>