Requiredif Constraint Throws Error

I am using cbvalidation-2.1.0+126 and coldbox-5.6.2.

I defined a validation rule in my Coldbox.cfc

validation = {
   sharedConstraints = {
     request ={
        'FirstName' = {required=true, requiredMessage='First name is required'},
        'LastName' = {required=true, requiredMessage='Last name is required'},
        'Email' = {requiredif= {'ContactMe':'Yes'}, requiredIfMessage='If you asked us to contact you please provide your email address'}

When I validate my form, I get the following error from cbvalidation\models\result\ValidationResult.cfc.
Type: string
Message: The value returned from the getValidationData function is not of type string.
Detail: If the component name is specified as a return type, it is possible that either a definition file for the component cannot be found or is not accessible.

The error appears to be related to using of the requiredif validation type. All of my other validation rules operate without a problem. Is there something wrong with my configuration definition?