code: public static String getNonEmptyStringParam(JSONObject params, String paramName) throws ApiException {
  		if (!params.containsKey(paramName)) {
  			throw new ApiException(Type.MISSING_PARAMETER, paramName);
  		}
  		String value = params.getString(paramName);
  		if (value == null || value.isEmpty()) {
  			throw new ApiException(Type.MISSING_PARAMETER, paramName);
  		}
  		return value;
  	}
docs: Gets the non empty string param with a given name and throws an exception accordingly if not
  found or empty.
  
  @param params the params
  @param paramName the param name
  @return the non empty string param
  @throws ApiException the api exception thown if param not found or string empty