title: PL SQL : NVL first parameter type conversion issue
body: <p>I have a table Application which has a column</p>
  
  <pre><code>BORROWINGTERM   NUMBER(10,0) Nullable
  </code></pre>
  
  <p>why this script throw an error (ORA-01722 invalid number)</p>
  
  <pre><code>select nvl(borrowingterm, 'no term') from Application 
  </code></pre>
  
  <p>while this one works</p>
  
  <pre><code>select nvl(to_char(borrowingterm), 'no term') from Application 
  </code></pre>
  
  <p>and this one also works</p>
  
  <pre><code>select nvl(1234,5678) from dual; 
  </code></pre>
  
  <p>base on <a href="http://www.techonthenet.com/oracle/functions/nvl.php" rel="noreferrer">this article</a></p>
  
  <p>the first parameter of NVL function should be string type</p>