title: @Pattern regex allowing only : numbers & empty String & numbers beginning by 0
body: <p>I'm using the @Pattern annotation on a String field in my Entity, with a regex allowing numbers or empty strings only, but I need to allow numbers beginning by 0 too.</p>
  
  <p>This is the pattern I'm using now :</p>
  
  <pre><code>//..
  @Pattern(message="Entrez un nombre" , regexp = "[+-]?(([1-9][0-9]*)|(0))([.,][0-9]+)?|(^$)")
  private String BSCId;
  //...
  </code></pre>
  
  <p>Thank you.</p>