Argument of type 'ProcessEnv' is not assignable to parameter of type 'DotenvPopulateInput'.
'string' index signatures are incompatible.
Type 'string | undefined' is not assignable to type 'string'.
Type 'undefined' is not assignable to type 'string'.ts(2345)
Seems that populate method just never worked in Typescript. process.env may contain an undefined value in dict, making it unassignable.
dotenv type: https://github.com/motdotla/dotenv/blob/cf4c56957974efb7238ecaba6f16e0afa895c194/lib/main.d.ts#L107C1-L109C2
node.js built-in type: