Unexpected error when paging

[jowerner]

When running a test case that includes the Paging action (e.g. TBrowse), the following log entries can be observed:

[13:40:41,709] INFO  [TBrowse-0] - ### Paging constructed...
[13:40:41,709] DEBUG [TBrowse-0] - # Paging - preValidateSafe()
[13:40:41,709] DEBUG [TBrowse-0] - XPATH Perf 0 ms - id('productOverview')
[13:40:41,720] DEBUG [TBrowse-0] - XPATH Perf 10 ms - //*[@id='productOverview']
[13:40:41,720] DEBUG [TBrowse-0] - Found 1 element(s) for XPath: //*[@id='productOverview']
[13:40:41,721] WARN  [TBrowse-0] - Unexpected error during prevalidation step, continuing without reporting an error
java.lang.NumberFormatException: For input string: ""
	at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
	at java.base/java.lang.Integer.parseInt(Integer.java:662)
	at java.base/java.lang.Integer.parseInt(Integer.java:770)
	at com.xceptance.posters.loadtest.actions.catalog.Paging.preValidate(Paging.java:97)
	at com.xceptance.xlt.api.actions.AbstractAction.preValidateSafe(AbstractAction.java:213)
	at com.xceptance.posters.loadtest.flows.BrowsingFlow.run(BrowsingFlow.java:100)
	at com.xceptance.posters.loadtest.tests.TBrowse.browsePosterStore(TBrowse.java:62)

The prevalidation code should throw an AssertionError to avoid the "Unexpected error ..." message.

Note that the paging probability may need to be set to 100 to reproduce this issue reliably.