After a discussion with @spicyj we decided to keep the warning even though the functions will throw in production. The warning is the only way to learn about that.

We should also document how to pass the secret through in case you know what you're doing.

function checkType(
    isRequired,
    props,
    propName,
    componentName,
    location,
    propFullName
  ) {
    componentName = componentName || ANONYMOUS;
    propFullName = propFullName || propName;
    if (props[propName] == null) {
      var locationName = ReactPropTypeLocationNames[location];
      if (isRequired) {
        if (props[propName] === null) {
          return new PropTypeError(
            `The ${locationName} \`${propFullName}\` is marked as required ` +
            `in \`${componentName}\`, but its value is \`null\`.`
          );
        }
        return new PropTypeError(
          `The ${locationName} \`${propFullName}\` is marked as required in ` +
          `\`${componentName}\`, but its value is \`undefined\`.`
        );
      }
      return null;
    } else {
      return validate(props, propName, componentName, location, propFullName);
    }
  }
  var chainedCheckType = checkType.bind(null, false);