Validation attribute for ensuring a collection has a minimum and maximum length

CollectionMinMaxLengthValidationAttribute.cs

public class CollectionMinMaxLengthValidationAttribute : ValidationAttribute
{
    const string errorMessage = "{0} must contain at least {1} item(s).";
    const string errorMessageWithMax = "{0} must contain between {1} and {2} item(s).";
    int minLength;
    int? maxLength;

    public CollectionMinMaxLengthValidationAttribute(int min)
    {
        minLength = min;
        maxLength = null;
    }

    public CollectionMinMaxLengthValidationAttribute(int min, int max)
    {
        minLength = min;
        maxLength = max;
    }

    //Override default FormatErrorMessage Method  
    public override string FormatErrorMessage(string name)
    {
        if (maxLength != null)
        {
            return string.Format(errorMessageWithMax, name, minLength, maxLength.Value);
        }
        return string.Format(errorMessage, name, minLength);
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        if (value == null && minLength == 0)
        {
            return ValidationResult.Success;
        }
        if (value == null && minLength > 0)
        {
            return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
        }

        var collection = ((IEnumerable)value).Cast<object>().ToList();
        if (collection.Count() >= minLength && (maxLength == null || collection.Count() <= maxLength))
        {
            return ValidationResult.Success;
        }
        return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
    }

}