title: If isset in apache ant is failing
body: <p>I am trying to check if a property exists in ant with the following:</p>
  
  <pre><code>&lt;target name="test"&gt;
      &lt;property name="testproperty" value="1234567890"/&gt;
      &lt;if&gt;
          &lt;isset property="testproperty"/&gt;
          &lt;then&gt;
              &lt;echo message="testproperty exists"/&gt;
          &lt;/then&gt;
          &lt;else&gt;
              &lt;echo message="testproperty does not exist"/&gt;
          &lt;/else&gt;
      &lt;/if&gt;
  &lt;/target&gt;
  </code></pre>
  
  <p>The result is a failure with the message:</p>
  
  <pre><code>build.xml:536: Problem: failed to create task or type if
  Cause: The name is undefined.
  Action: Check the spelling.
  Action: Check that any custom tasks/types have been declared.
  Action: Check that any &lt;presetdef&gt;/&lt;macrodef&gt; declarations have taken place.
  </code></pre>
  
  <p>I must be doing something wrong with isset as the following runs smoothly:</p>
  
  <pre><code>&lt;target name="test"&gt;
      &lt;property name="testproperty" value="1234567890"/&gt;
      &lt;echo message="'${testproperty}'"/&gt;
  &lt;/target&gt;
  </code></pre>
  
  <p>Please advice :)</p>