SoapUI NG Pro - Empty Expected Result in XPath Match results in passed Assertion

Pre-Condition:

- Valid XML Response

Steps:

1. Add a "Xpath Match Assertion"

2. Enter a valid Xpath Expression which fits the given reply (click on "select from current test" would return acutal value in Expected Result)

3. Delete any String which is entered in "Expected Result"

4. Run test

Expected Result:

- Assertion Failed, because given Expression is not empty

Acutal Result:

- Assertion Passed

Tested with 1.5.0 and 1.6.0