title: Force JPA to remove NOT NULL flag after boxing the Entity field
body: <p>I use Hibernate with Java, and at some point I had the following entity (simplified):</p>
  
  <pre><code>@Entity
  public class A {
      private int value;
  };
  </code></pre>
  
  <p>I had this class for a long time, and, of course, some rows were added to the database.
  But, soon, I changed int to <code>Integer</code>(to support nullable on that column).<br/>
  Now, it looks like as follow:</p>
  
  <pre><code>@Entity
  public class A {
      private Integer value;
  };
  </code></pre>
  
  <p>When JPA creates the column for the <code>Integer</code> it makes column <code>nullable</code>, but when creates column for <code>int</code>, that column has property <code>NOT NULL</code>. And that's the same for all boxed types in Java.</p>
  
  <p>But, when I run my app, JPA doesn't remove the <code>NOT NULL</code> flag from the already defined schema of the table in the database.
  I know that I may remove it manually, but, unfortunately, I described <strong>very</strong> simplified example, and in the real life I have a lot of similar classes with the similar properties.</p>
  
  <p>So, how to force JPA to update the schema correctly and don't loose data already created?</p>