New Post: Optional Image and Page Field on Custom Data Type

Additional Info for this case:
If I remove the ForeignKey Attributes on all the mentioned fields, I can save the entity correctly, but after close and re-open, I 'll get an error and in the Server Log the following error messages appear:

System.InvalidOperationException: Field 'BackgroundImageUrl' on type 'Iba.CompositeC1.Functions.DataTypes.IListDataEntry,Iba.CompositeC1.Functions' is null, does not allow null and does not have a default value
   at Composite.C1Console.Workflow.WorkflowFacadeImpl.RunWorkflow(Guid instanceId)
   at Composite.C1Console.Workflow.WorkflowFacadeImpl.RunWorkflow(WorkflowInstance workflowInstance)
   at Composite.C1Console.Workflow.WorkflowActionExecutor.Execute(String serializedEntityToken, String serializedActionToken, ActionToken actionToken, FlowControllerServicesContainer flowControllerServicesContainer)
   at Composite.C1Console.Actions.ActionExecutorFacade.Execute(IActionExecutorSerializedParameters actionExecutor, String serializedEntityToken, String serializedActionToken, ActionToken actionToken, FlowControllerServicesContainer flowControllerServicesContainer)
   at Composite.C1Console.Actions.ActionExecutorFacade.Execute(EntityToken entityToken, ActionToken actionToken, FlowControllerServicesContainer flowControllerServicesContainer, TaskManagerEvent taskManagerEvent)
   at Composite.Core.WebClient.FlowMediators.ActionExecutionMediator.ExecuteElementAction(ElementHandle elementHandle, ActionHandle actionHandle, String consoleId)
   at Composite.Core.WebClient.FlowMediators.TreeServicesFacade.ExecuteElementAction(String providerName, String serializedEntityToken, String piggybag, String serializedActionToken, String consoleId)
   at Composite.Services.TreeServices.ExecuteSingleElementAction(ClientElement clientElement, String serializedActionToken, String consoleId) in d:\Git\IBA\newiba.ch\Iba.CompositeC1.Web\Composite\services\Tree\TreeServices.asmx:line 211

System.InvalidOperationException: Field 'BackgroundImageUrl' on type 'Iba.CompositeC1.Functions.DataTypes.IListDataEntry,Iba.CompositeC1.Functions' is null, does not allow null and does not have a default value
   at Composite.Data.DynamicTypes.DataTypeDescriptorFormsHelper.GetBindings(IData dataObject, Boolean allowMandatoryNonDefaultingProperties)
   at Composite.Data.DynamicTypes.DataTypeDescriptorFormsHelper.UpdateWithBindings(IData dataObject, Dictionary`2 bindings)
   at Composite.C1Console.Elements.ElementProviderHelpers.AssociatedDataElementProviderHelper.EditAssociatedDataWorkflow.editDataCodeActivity_ExecuteCode(Object sender, EventArgs e)
   at System.Workflow.ComponentModel.Activity.RaiseEvent(DependencyProperty dependencyEvent, Object sender, EventArgs e)
   at System.Workflow.Activities.CodeActivity.Execute(ActivityExecutionContext executionContext)
   at System.Workflow.ComponentModel.ActivityExecutor`1.Execute(T activity, ActivityExecutionContext executionContext)
   at System.Workflow.ComponentModel.ActivityExecutorOperation.Run(IWorkflowCoreRuntime workflowCoreRuntime)
   at System.Workflow.Runtime.Scheduler.Run()

System.InvalidOperationException: Field 'BackgroundImageUrl' on type 'Iba.CompositeC1.Functions.DataTypes.IListDataEntry,Iba.CompositeC1.Functions' is null, does not allow null and does not have a default value
   at Composite.Data.DynamicTypes.DataTypeDescriptorFormsHelper.GetBindings(IData dataObject, Boolean allowMandatoryNonDefaultingProperties)
   at Composite.Data.DynamicTypes.DataTypeDescriptorFormsHelper.UpdateWithBindings(IData dataObject, Dictionary`2 bindings)
   at Composite.C1Console.Elements.ElementProviderHelpers.AssociatedDataElementProviderHelper.EditAssociatedDataWorkflow.editDataCodeActivity_ExecuteCode(Object sender, EventArgs e)
   at System.Workflow.ComponentModel.Activity.RaiseEvent(DependencyProperty dependencyEvent, Object sender, EventArgs e)
   at System.Workflow.Activities.CodeActivity.Execute(ActivityExecutionContext executionContext)
   at System.Workflow.ComponentModel.ActivityExecutor`1.Execute(T activity, ActivityExecutionContext executionContext)
   at System.Workflow.ComponentModel.ActivityExecutorOperation.Run(IWorkflowCoreRuntime workflowCoreRuntime)
   at System.Workflow.Runtime.Scheduler.Run()

Thanks in advance for any help.

Best regards,
Chris