Fix IllegalStateException: No logical node selected!

[matthias-ronge]

Exception occurs when opening Metadata Editor, because calling method expects null in no-data case, but receives IllegalStateException:

[solth]

I think this can potentially create a NullPointerException because the result of DataEditorService.getStructuralElementView is also passed as last parameter to ProcessService.findLinkableChildProcesses where .contains is called on it without a null-check:

kitodo-production/Kitodo/src/main/java/org/kitodo/production/services/data/ProcessService.java

Line 785 in 3d4fd47

if (allowedStructuralElementTypes.contains(getBaseType(process.getId()))) {

[matthias-ronge]

No, because allowedSubstructuralElements is the result of Map.keySet() which cannot be null.

BTW, this is not the problem here. The problem was that the calling method expects null in case there is nothing (and there are severeal more correct return null; statements below in getStructuralElementView()), but in this one place the function throws an IllegalStateException instead of returning null.