How/where to download SOAP-UI sources?

Thanks!

Unfortunately, when trying to build, there are tons of UnitTest-errors:

[ERROR] Tests run: 683, Failures: 259, Errors: 0, Skipped: 14, Time elapsed: 13.126 s <<< FAILURE! - in TestSuite
[ERROR] createMockAsWar on createMockAsWar(com.eviware.soapui.actions.MockAsWarActionTest)(com.eviware.soapui.actions.MockAsWarActionTest)  Time elapsed: 1.779 s  <<< FAILURE!
java.lang.ExceptionInInitializerError
        at com.eviware.soapui.actions.MockAsWarActionTest.setUpFormDialog(MockAsWarActionTest.java:64)
        at com.eviware.soapui.actions.MockAsWarActionTest.setUp(MockAsWarActionTest.java:60)
Caused by: java.lang.reflect.InaccessibleObjectException: Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @59e5ddf
        at com.eviware.soapui.actions.MockAsWarActionTest.setUpFormDialog(MockAsWarActionTest.java:64)
        at com.eviware.soapui.actions.MockAsWarActionTest.setUp(MockAsWarActionTest.java:60)

[ERROR] builderValuesShouldMatchModel[0 - class com.eviware.soapui.impl.wsdl.panels.teststeps.amf.AMFRequestTestStepPanelBuilder] on builderValuesShouldMatchModel[0 - class com.eviware.soapui.impl.wsdl.panels.teststeps.amf.AMFRequestTestStepPanelBuilder](com.eviware.soapui.impl.GenericPanelBuilderTest)(com.eviware.soapui.impl.GenericPanelBuilderTest)  Time elapsed: 0.004 s  <<< FAILURE!
java.lang.NoClassDefFoundError: Could not initialize class org.mockito.internal.creation.jmock.ClassImposterizer$3
        at com.eviware.soapui.impl.GenericPanelBuilderTest.<init>(GenericPanelBuilderTest.java:95)

The latter repeats a hundred times or so.

"java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @59e5ddf" sounds like a Java version issue to me. Has this really ever been built with Java 16 (as the projects home-page "SmartBear/soapui: SoapUI is a free and open source cross-platform functional testing solution for APIs and web services. (github.com)" suggests?)