handle blank enum

[stefanprobst]

i am getting the following from a django restframework generated openapi doc:

components:
  schemas:
    BlankEnum:
      enum:
        - ''
    NullEnum:
      enum:
        - null

which this generator transforms into:

// src/api/models/BlankEnum.ts
export enum BlankEnum {
    = '',
}

and

// src/api/models/NullEnum.ts
export type NullEnum = {
};

note how src/api/models/BlankEnum.ts is invalid syntax and causes a compile error

[alexdanielyan]

I downgraded to ^0.20.1 and it works in that version

"openapi-typescript-codegen": "^0.20.1",