SoapUI OpenSoure - NullPointerException at com.eviware.soapui.impl.wsdl.WsdlProject.reload

I am trying to implement an automatic reload after updating the WSDL in my project but I keep getting a null pointer although the path is correct and the project exists. I've seen some old posts on the internet but it seems to me the provided solutions are only for the SoapUI Pro. Is that right? How could I get my code working on the SoapUi Open Source 5.3.0?

Partial code:

void reloadWsdlProject(Object log) {
	try	{
		log.info ("Checking project absolute path [" + wsdlProject.getPath() + "]");
		wsdlProject.reload( wsdlProject.getPath() );
	} catch( SoapUIException ex ) {
		log.error( ex );
	}
}       

Error:

2017-03-06 14:52:33,514 ERROR [errorlog] java.lang.NullPointerException
java.lang.NullPointerException
	at com.eviware.soapui.impl.wsdl.WsdlProject.reload(WsdlProject.java:1353)
	at com.eviware.soapui.impl.wsdl.WsdlProject$reload.call(Unknown Source)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:45)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:108)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
	at UpdateWsdls.reloadWsdlProject(Script11.groovy:355)
	at UpdateWsdls$reloadWsdlProject.call(Unknown Source)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:45)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:108)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
	at Script11.run(Script11.groovy:372)
	at com.eviware.soapui.support.scripting.groovy.SoapUIGroovyScriptEngine.run(SoapUIGroovyScriptEngine.java:90)
	at com.eviware.soapui.impl.wsdl.teststeps.WsdlGroovyScriptTestStep.run(WsdlGroovyScriptTestStep.java:141)
	at com.eviware.soapui.impl.wsdl.panels.teststeps.GroovyScriptStepDesktopPanel$RunAction$1.run(GroovyScriptStepDesktopPanel.java:250)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)