code: public void setInput(final String inputPath) {
          if (inputPath == null) {
              throw (new IllegalArgumentException(
                      "You must provide a source folder or file"));
          }
          File inputFile = new File(inputPath);
          if (inputFile.exists()) {
              if (inputFile.isDirectory() && inputFile.list().length == 0) {
                  throw new IllegalArgumentException("Folder '" + inputPath
                          + "' is empty");
              }
          } else {
              throw new IllegalArgumentException("Input file or folder '"
                      + inputPath + "' not found");
          }
          this.input = inputFile;
      }
docs: Check the input parameter and keep it only if it is valid.
  
  @param inputPath a file or folder name (relative or absolute)