Problems: Nestjs config service with optional environment variables
Return value from ConfigService.get is string undefined
When the validate function returns an object where a key, e.g. OPT, is undefined, assignVariablesToProcess will assign undefined to process.env.OPT which will stringify it (see https://nodejs.org/api/process.html#processenv). This results in ConfigService.get returning process.env.OPT which now has the value 'undefined'.
Reproduce
yarn run start and observe the log.
Return type from ConfigService<EnvironmentVariables, true>.get excludes undefined
The second generic parameter (WasValidated) changes the return value of ConfigService.get. If true, it removes undefined from the return type. If false, it adds undefined. The problem here is that a value could be both validated and undefined.
Reproduce
Observe the TypeScript return type of optValue in main.ts.