title: spring validator @Pattern doesn't work on Integer
body: <p>I am trying a simple pattern validation:</p>
  
  <pre><code>@Min(value = 0, message = "invalid.amount")
  @Pattern(regexp = "[0-9]+", message = "invalid.amount")
  private double amount;
  </code></pre>
  
  <p>But it gives the error like: </p>
  
  <pre><code>org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree.throwExceptionForNullValidator(ConstraintTree.java:229)
  </code></pre>
  
  <p>But this works perfectly fine:</p>
  
  <pre><code>@Pattern(regexp = "[\\w|-]{1,5}")
  private String data;
  </code></pre>
  
  <p>It seems regex doesn't work on number types.</p>