title: "is an unknown property": custom properties in Spring's application.properties
body: <p>Sorry if this a trivial thing, I'm hacking out on an abandoned project and trying to add a custom property to the projects <code>application.properties</code> file.</p>
  
  <p>The properties actually work fine (i.e. they are properly resolved when doing <code>@Value("${foo.config.someValue"})</code>) but Eclipse insists on telling me this:</p>
  
  <p><a href="https://i.stack.imgur.com/gRDKd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gRDKd.png" alt="enter image description here"></a></p>
  
  <p>Pressing tab does nothing at all.</p>
  
  <p>How can I make this go away? Can I define my custom properties somewhere? Or maybe this isn't the way at all to add custom configuration properties?</p>