refactor: catch NPE to make xml systemID parsing more stable (planning#1151)

client/src/main/java/dev/fitko/fitconnect/core/validation/xml/SchemaIdentifier.java

@@ -17,7 +17,7 @@ public class SchemaIdentifier {
     private String getSchemaName(String name) {
         try {
             return Path.of(name).getFileName().toString();
-        } catch (InvalidPathException e) {
+        } catch (InvalidPathException | NullPointerException e) {
             return null;
         }
     }