@Nullable
 private BaseNameError checkBaseName(final String baseNameCandidate) {
   for (PropertiesFile propertiesFile : myPropertiesFiles) {
     final String name = propertiesFile.getVirtualFile().getName();
     if (!name.startsWith(baseNameCandidate)
         || !PropertiesUtil.BASE_NAME_BORDER_CHAR.contains(
             name.charAt(baseNameCandidate.length()))) {
       return new BaseNameError(name);
     }
   }
   return null;
 }