If an expression returns a method that returns void then the result is treated as null.

Example

Given we have the following method in our fixture code:

public void myVoidMethod() {
    ...
}

Then the following markup will cause a SUCCESS to be reported, since no return value can be obtained from myVoidMethod() the result is taken to be null:

<span concordion:assertEquals="myVoidMethod()">(null)</span>

And, to demonstrate a counter-example, the following markup will report a FAILURE:

<span concordion:assertEquals="myVoidMethod()">xyz</span>

Void Result

Example