title: Cannot convert value of type 'String.Type' to expected argument type 'String!'
body: <p>I am using a library MDWamp written in objective C and it has a property of the following type</p>
  
  <pre><code>@property (nonatomic, strong) void (^deferredWampCRASigningBlock)( NSString *challange, void(^finishBLock)(NSString *signature) );
  </code></pre>
  
  <p>This is the signature in swift</p>
  
  <pre><code>public var deferredWampCRASigningBlock: ((String!, ((String!) -&gt; Void)!) -&gt; Void)!
  </code></pre>
  
  <p>and when I try to instantiate it in swift in the following manner</p>
  
  <pre><code>self.wamp?.config.deferredWampCRASigningBlock?(str : String , { (str2 : String) -&gt; Void in
  
          })
  </code></pre>
  
  <p>but I get this error </p>
  
  <blockquote>
    <p>Cannot convert value of type 'String.Type' to expected argument type
    'String!'</p>
  </blockquote>
  
  <p>Any suggestions would be appreciated.</p>