title: ios navigation error using button
body: <p>I am trying to go from  login screen to signup. But getting error...</p>
  
  <blockquote>
    <p>Terminating app due to uncaught exception
    'NSInvalidArgumentException', reason: 'Application tried to present a
    nil modal view controller on target .'</p>
  </blockquote>
  
  <p>Login.H</p>
  
  <pre><code>#import "SignupController.h"
  
  @interface LoginController : UIViewController {
  
  IBOutlet SignupController *signupController;
  </code></pre>
  
  <p>Login.M</p>
  
  <pre><code>(IBAction)signup:(UIButton*) sender
  {
      NSLog(@"lla"); 
          [self presentModalViewController:signupController animated:YES];
  
  }
  </code></pre>