Fixes issue#1636

Some frameworks (e.g. django rest framework, I guess) generate following schema:

openapi: 3.0.3info:    version: 1.0.0components:    schemas:        BlankEnum:            enum:                - ''

right now this library generates invalid typescript:

export enum BlankEnum {     = '',}

This happens ingetEnum functions that don't check for invalid input (getEnum([''])) in our case.

I decided to give such enum valuesBLANK name so that generated files are correct

export enum BlankEnum {    BLANK = '',}

Not sure if it would be a better idea to just omit these values (I mean, the name saysBlankEnum) but everything's better than broken syntax