code: public static double nonNegative(final double value, final String message) {
  		if (value < 0) {
  			throw new IllegalArgumentException(format(
  				"%s must not be negative: %f.", message, value
  			));
  		}
  		return value;
  	}
docs: Check if the specified value is not negative.
  
  @param value the value to check.
  @param message the exception message.
  @return the given value.
  @throws IllegalArgumentException if {@code value < 0}.