If you make a library with a function and a GUI editor for the function, and you keep one control nullable, like this...

<editor>
  <appliesto>(function)test</appliesto>
  <display>Test</display>
  <category>Tests</category>
  <create>test ("")</create>
  <add>Test</add>

  <control>
    <controltype>expression</controltype>
    <simple>text</simple>
    <attribute>0</attribute>
  </control>

  <control>
    <controltype>expression</controltype>
    <simple>text</simple>
    <attribute>1</attribute>
    <nullable/>
    <breakbefore/>
  </control>
</editor>

...Why does Quest throw an error ('Error running script: Too few parameters passed to test function - only 1 passed, but 2 expected') if you don't add another parameter?

Is <nullable/> only for specific functions?