title: Error when I try to add a dateTime field to my table
body: <p>I am trying to add a new "dateTime" field to my posts table :</p>
  
  <pre><code>public function up()
      {
          Schema::table('posts', function (Blueprint $table) {
  
              $table-&gt;dateTime('published_at');
  
          });
      }
  </code></pre>
  
  <p>but when I execute <code>php artisan migrate</code> I get the error :</p>
  
  <pre><code>[Illuminate\Database\QueryException]                                                                                                     
    SQLSTATE[23502]: Not null violation: 7 ERROR:  column "published_at" contains null values (SQL: alter table "posts" add column "publish  
    ed_at" timestamp(0) without time zone not null)  
  
  
  
  
  [PDOException]                                                                             
  
        SQLSTATE[23502]: Not null violation: 7 ERROR:  column "published_at" contains null values
  </code></pre>
  
  <p>What's wrong here ?</p>