There is no clear error when adding "Named" property to an object that is not stored

[nicolasdemauroy]

When adding a "Named" property to a non-stored object, there is an unclear Exception. It should be tested before and given a clear exception to the developer

SEVERE   51:44.926 Exception class java.lang.NullPointerException - null
SEVERE   51:44.927  - org.openlowcode.design.data.DataObjectDefinition.generateToFile(DataObjectDefinition.java:4450)
SEVERE   51:44.927  - org.openlowcode.design.module.Module.generateSources(Module.java:2068)
SEVERE   51:44.927  - org.openlowcode.design.module.Module.main(Module.java:2268)