title: Check if not null or not 0 in Liquibase Precondition
body: <p>I have currently an issue with liquibase preconditions.
  I would like to insert something only if a precondition request does'nt answer 0 or null... I explain : </p>
  
  <pre><code>&lt;changeSet id="myId" author="myName"&gt;
  &lt;preConditions onFail="MARK_RAN"&gt;
      &lt;sqlCheck expectedResult=????&gt;SELECT COUNT(1) FROM tableB WHERE column2 IS NOT NULL;
      &lt;/sqlCheck&gt;
  &lt;/preConditions&gt;
  &lt;insert tableName="tableA"&gt;
      &lt;column name="column1" valueComputed="(SELECT columnA FROM tableB WHERE columnB IS NOT NULL;)" /&gt;
      &lt;column name="column2" valueComputed="(SELECT columnB FROM tableB WHERE columnB IS NOT NULL;)" /&gt;
  &lt;/insert&gt;
  </code></pre>
  
  <p></p>
  
  <p>I would like for my changeSet to only be played if the first request give me a result. Is there a way to do that without a custom precondition ? </p>
  
  <p>Thanks in advance</p>