[BUG] Description

Description

When generating enums from the swagger definition, null options get turned into string instead of staying plain null. The issue is when i select the null option it actually a string and not null thus i can't send it to the backend w/o setting it to null.

openapi-generator version

5.0.0

OpenAPI declaration file content or url

"reason": {
    "type": "string",
        "enum": [
            "one",
            "two",
            null
        ],
    "nullable": true
}, 

Steps to reproduce

run generator with swagger file containing the enum above
openapi-generator-cli generate -g typescript-angular -o ./openapi --additional-properties disallowAdditionalPropertiesIfNotPresent=false,ngVersion=10.2.4,fileNaming=kebab-case -i

This should produce an enum like

export type ReasonEnum = 'one' | 'two' | 'null';
export const ReasonEnum = {
        One: 'one' as ReasonEnum,
        Two: 'two' as ReasonEnum,
        Null: 'null' as ReasonEnum
};

Related issues/PRs

a similar bug has bin reported back in 2019 https://github.com/OpenAPITools/openapi-generator/issues/1997

Suggest a fix

The produced enum should convert null like (not a string, just plain null)

Null: null as ReasonEnum

Start with the openapi-generator-cli generate entry point using the provided OpenAPI declaration and the typescript-angular generator. Inspect the generated ReasonEnum and trace how the null enum value is rendered; done means the generated type and constant preserve null as a plain null rather than the string 'null'.