fix: prevent error when create deposit manually

AoU-Admin/src/main/java/ch/unige/aou/controller/admin/PublicationController.java

@@ -112,13 +112,16 @@ public class PublicationController extends AouResourceController<Publication> {
     this.eventService.createEvent(publication, EventType.PUBLICATION_CREATED);
 
     // try to import file if possible
-    switch (publication.getImportSource()) {
-      case ARXIV:
-        this.arxivImportService.createDocumentFileFromArxivMetadata(publication);
-        break;
-      case DOI:
-        this.doiCrossrefImportService.createDocumentFileFromCrossrefMetadata(publication);
-        break;
+    Publication.ImportSource importService = publication.getImportSource();
+    if (importService != null) {
+      switch (importService) {
+        case ARXIV:
+          this.arxivImportService.createDocumentFileFromArxivMetadata(publication);
+          break;
+        case DOI:
+          this.doiCrossrefImportService.createDocumentFileFromCrossrefMetadata(publication);
+          break;
+      }
     }
 
     return response;