Clarify `allowEmptyValue`

From the specification it is a little ambiguous what the allowEmptyValue entails, notably what empty means:

• is a string containing only whitespaces considered empty?
• does it only affect a query parameter when its value is of type: string? Or would 0, false, [] or {} qualify as empty when a query parameter is of another type?

[webron]

So here’s the clarification, and we can add more information in the spec if needed.

allowEmptyValue means a zero-length value can be provided. This translates to ?exampleParam= and not ?exampleParam. There is no way to describe ?exampleParam, and from what I recall in our discussions on this topic, many @OAI/tsc members claimed that such a thing doesn’t really exist.

Combining allowEmptyValue with minLength=10 is meaningless as given you are defining a minimum length, 0 isn’t it. Only the minLength will actually take effect here.

As for the follow-up question: yes, a required parameter can allow empty values, there’s no contradiction there.

[MikeRalphson]

@darrelmiller although these relate to OAS 2.0 - two (and only two) Microsoft Azure API definitions specifiy allowEmptyValue: true. These are:

• applicationinsights/resource-manager/microsoft.insights/stable/2015-05-01/favorites_API
• trafficmanager/resource-manager/Microsoft.Network/preview/2017-09-01-preview/trafficmanageranalytics

Perhaps reaching out to find the intent of using the flag in these cases might be an interesting data point?

Only two other API definitions across the whole of APIs.guru (1,400+ definitions) use allowEmptyValue so it certainly does not seem to be widely adopted in public APIs.