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.

switch (typeof propValue) {
    case 'number':
    case 'string':
    case 'undefined':
      return true;
    case 'boolean':
      return !propValue;
    case 'object':
      if (Array.isArray(propValue)) {
        return propValue.every(isNode);
      }
      if (propValue === null || ReactElement.isValidElement(propValue)) {
        return true;
      }
      var iteratorFn = getIteratorFn(propValue);
      if (iteratorFn) {
        var iterator = iteratorFn.call(propValue);
        var step;
        if (iteratorFn !== propValue.entries) {
          while (!(step = iterator.next()).done) {
            if (!isNode(step.value)) {
              return false;
            }
          }
        } else {
          
          while (!(step = iterator.next()).done) {
            var entry = step.value;
            if (entry) {