title: Fluent Validation only if value is supplied
body: <p>I have a Post method and based on the data Posted I will return a result. I want to perform validation only if the fields are supplied. If no value is posted I do not want to perform the validation. This is what I have currently. Obviously if the value is null it will crash as it expects a value, how can I solve this?</p>
  
  <pre><code>public bool IsValidAvailability(int AvailabiltyValue)
  {
      if (AvailabiltyValue &gt; AvailabilityMax || AvailabiltyValue &lt; AvailabilityMin)
          return false;
      return true;
  }
  </code></pre>
  
  <p>This is my Rules for the validation. Can I add anything to make this validation below happen only if the value is supplied?</p>
  
  <pre><code>RuleFor(x =&gt; (int)x.Availability).Must(validatorServices.IsValidAvailability).WithMessage("Availability must be between " + validatorServices.AvailabilityMin + " and " + validatorServices.AvailabilityMax);
  </code></pre>