Suppress one of the validation errors from `allow_blank` on a required parameter

Using allow_blank validator for the required parameter may lead to two validation errors, but I expected to have only one.

Example:

requires :customer_key, type: String, allow_blank: false

If there is no customer_key parameter in request then we receive the following Grape::Exceptions::ValidationErrors exception:

error
=> #<Grape::Exceptions::ValidationErrors: Grape::Exceptions::ValidationErrors>

error.errors
=> {["customer_key"]=>[#<Grape::Exceptions::Validation: is missing>, #<Grape::Exceptions::Validation: is empty>]}

So we receive

• one error because the required parameter "is missing" and
• another one caused by allow_blank validator because the parameter "is empty"

The second error (produced by the allow_blank) doesn't make sense and looks a bit annoying. The expected behavior is to receive only "is missing" error.

Reproduce the example request using requires :customer_key, type: String, allow_blank: false, then trace the validation handling for a missing parameter. Done means the resulting Grape::Exceptions::ValidationErrors contains only the “is missing” validation and no duplicate “is empty” error.