- Limit the depth of subdirectories to process in BulkImport.

- Code polishing.

src/main/java/eu/openaire/urls_controller/services/BulkImportServiceImpl.java

@@ -449,7 +449,7 @@ public class BulkImportServiceImpl implements BulkImportService {
     public List<String> getFileLocationsInsideDir(String directory)
     {
         List<String> fileLocations = null;
-        try ( Stream<Path> walkStream = Files.find(Paths.get(directory), Integer.MAX_VALUE, (filePath, fileAttr) -> fileAttr.isRegularFile()) )
+        try ( Stream<Path> walkStream = Files.find(Paths.get(directory), 20, (filePath, fileAttr) -> fileAttr.isRegularFile()) )
         // In case we ever include other type-of-Files inside the same directory, we need to add this filter: "&& !filePath.toString().endsWith("name.ext")"
         {
             fileLocations = walkStream.map(Path::toString).collect(Collectors.toList());
@@ -471,9 +471,8 @@ public class BulkImportServiceImpl implements BulkImportService {
             md5 = DatatypeConverter.printHexBinary(md5MD.digest()).toLowerCase();
         } catch (Exception e) {
             logger.error("Error when getting the MD5-hash for: " + string, e);
-            return null;
         }
-        return md5;
+        return md5; // It may be null.
     }
 
 
@@ -487,7 +486,7 @@ public class BulkImportServiceImpl implements BulkImportService {
             id = id.toLowerCase();
 
         String idMd5Hash = getMD5Hash(id);
-        if ( idMd5Hash == null )
+        if ( idMd5Hash == null )    // The error is logged inside.
             return null;
 
         return (datasourcePrefix + "::" + idMd5Hash);