code: protected void checkFileExists( String... existingFilePath ) {
          StringBuilder sb = null;
          for( String filePath : existingFilePath ) {
              File file = new File(filePath);
              if (!file.exists()) {
                  if (sb == null) {
                      sb = new StringBuilder();
                      sb.append("The following file doesn't seem to exist: ");
                  }
                  sb.append("\n\t").append(file.getAbsolutePath());
              }
          }
          if (sb != null)
              throw new ModelsIllegalargumentException(sb.toString(), this.getClass().getSimpleName(), pm);
      }
docs: Checks if passed path strings exist on the filesystem. If not, an Exception is thrown.
  
  @param existingFilePath one or more file paths that need to exist.