[BUG] [Elm] Enums getting extra value with "UnknownEnumVariableName"

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?

• Using the full Stripe API spec.

• Have you validated the input using an OpenAPI validator (example)?

• I used the CLI with validate and it found no issues.

• Have you tested with the latest master to confirm the issue still exists?

• Yes

• Have you searched for related issues/PRs?

Description

openapi-generator version

Latest master

OpenAPI declaration file content or url

https://raw.githubusercontent.com/stripe/openapi/master/openapi/spec3.json

Generation Details

java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate    -i https://raw.githubusercontent.com/stripe/openapi/master/openapi/spec3.json    -g elm    -o ./elm-stripeFix

Some enum types turn into a custom type with a bogus constructor:

type TaxExempt
    = TaxExemptUnknownEnumVariableName
    | TaxExemptExempt
    | TaxExemptNone
    | TaxExemptReverse


taxExemptVariants : List TaxExempt
taxExemptVariants =
    [ TaxExemptUnknownEnumVariableName
    , TaxExemptExempt
    , TaxExemptNone
    , TaxExemptReverse
    ]


stringFromTaxExempt : TaxExempt -> String
stringFromTaxExempt model =
    case model of
        TaxExemptUnknownEnumVariableName ->
            ""

        TaxExemptExempt ->
            "exempt"

        TaxExemptNone ->
            "none"

        TaxExemptReverse ->
            "reverse"

... but "TaxExemptUnknownEnumVariableName" does not exist, and the spec json does not seem to indicate any other values besides the valid three...

Run the Elm generation command in the issue against the linked Stripe OpenAPI spec and inspect the generated TaxExempt type, variants list, and stringFromTaxExempt function. Trace the Elm generator entry point that handles enum values and compare the output with the three values in the spec. Done means no UnknownEnumVariableName constructor or empty-string mapping is generated.