code: public Number getNumber(String key) throws NumberFormatException {
          String value = getString(key);
          if (value == null) {
              return null;
          }
          else {
              try {
                  return Integer.valueOf(value);
              }
              catch (NumberFormatException e) {
              }
              try {
                  return Long.valueOf(value);
              }
              catch (NumberFormatException e) {
              }
              return Double.valueOf(value);
          }
      }
docs: Returns null if the given key isn't in this PropertyMap.
  
  @param key Key of property to read