org.ametys.runtime.model.exception.UndefinedItemPathException: Unable to retrieve the model item at path 'myAttributeInTheAddedMixin'. This path is not defined by the model.
	at org.ametys.runtime.model.ModelHelper.getModelItem(ModelHelper.java:109)
	at org.ametys.plugins.repository.data.holder.impl.DefaultModelAwareDataHolder.getDefinition(DefaultModelAwareDataHolder.java:331)
	at org.ametys.plugins.repository.data.holder.impl.DefaultModelAwareDataHolder.getValue(DefaultModelAwareDataHolder.java:214)
	at org.ametys.plugins.repository.data.ametysobject.ModelAwareDataAwareAmetysObject.getValue(ModelAwareDataAwareAmetysObject.java:64)
	at my.package.MyCreateContentFunction._populateContent(MyCreateContentFunction.java:291)
	at my.package.MyCreateContentFunction.execute(MyCreateContentFunction.java:123)
	at jdk.internal.reflect.GeneratedMethodAccessor45.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.ametys.runtime.plugin.component.PluginsComponentManager$ComponentInvocationHandler.invoke(PluginsComponentManager.java:177)
	at com.sun.proxy.$Proxy20.execute(Unknown Source)
	at com.opensymphony.workflow.AbstractWorkflow.executeFunction(AbstractWorkflow.java:871)
	at com.opensymphony.workflow.AbstractWorkflow.transitionWorkflow(AbstractWorkflow.java:1044)
	at org.ametys.plugins.workflow.AbstractAmetysWorkflow.transitionWorkflow(AbstractAmetysWorkflow.java:212)
	at com.opensymphony.workflow.AbstractWorkflow.initialize(AbstractWorkflow.java:618)
	at org.ametys.plugins.workflow.AbstractAmetysWorkflow.initialize(AbstractAmetysWorkflow.java:99)
	at org.ametys.cms.workflow.ContentWorkflowHelper._doInitialize(ContentWorkflowHelper.java:223)
	at org.ametys.cms.workflow.ContentWorkflowHelper.createContent(ContentWorkflowHelper.java:191)
[...]

    protected void _populateContent(Map transientVars, ModifiableContent content) throws WorkflowException
    {
        super._populateContent(transientVars, content);
        content.setValue("myAttributeInTheAddedMixin", MY_VALUE);
    }