Accessing legacy UI in afterNavigation of page with parameter causes IllegalArgumentException

The legacy UI.getCurrent() works under MPR differently than normal. It will trigger creation of new UI instance. Now that seems to trigger some activity in Router as well, as it needs to check for @LegacyUI annatotation. Now it is that process that triggers the exception. Whether this is a design limitation or not, I do not know yet.

java.lang.IllegalArgumentException: Navigation target 'org.vaadin.mprdemo.PageWithParameter' requires a parameter.
    at com.vaadin.flow.router.internal.HasUrlParameterFormat.checkMandatoryParameter(HasUrlParameterFormat.java:272)
    at com.vaadin.flow.router.internal.AbstractRouteRegistry.getTargetUrl(AbstractRouteRegistry.java:281)
    at com.vaadin.flow.server.SessionRouteRegistry.getTargetUrl(SessionRouteRegistry.java:198)
    at com.vaadin.mpr.core.PathResolver.findPathString(PathResolver.java:78)
    at com.vaadin.mpr.core.PathResolver.getTopNavigationTarget(PathResolver.java:43)
    at com.vaadin.mpr.core.AbstractMprUIProvider.getLegacyUI(AbstractMprUIProvider.java:79)
    at com.vaadin.mpr.core.AbstractMprServlet.getCurrentUI(AbstractMprServlet.java:99)
    at com.vaadin.util.CurrentInstance.get(CurrentInstance.java:90)
    at com.vaadin.ui.UI.getCurrent(UI.java:936)
    at org.vaadin.mprdemo.PageWithParameter.afterNavigation(PageWithParameter.java:30)

You can workaround this using @OptionalParameter

    @Override
    public void setParameter(BeforeEvent beforeEvent, @OptionalParameter String name) {
        this.name = name;
    }

This issue is not limited to Vaadin version 14.7.5

vaadin / multiplatform-runtime

Accessing legacy UI in afterNavigation of page with parameter causes IllegalArgumentException #103