title: Nunjucks check for object or string
body: <p>How can I check if a variable is an object or string in an if block? 
  It seems one can not call functions inside the <code>{% if ... %}</code> block.
  And the other <code>{{ if() }}</code> syntax seems only to be for inline conditions.</p>
  
  <p>I solve it now to test for some object properties that should be there when the variable is an object, but there should be a better solution. Like an <code>isObject</code> or <code>isString</code> function</p>