Proxy that override toString() could lead to TypeError from indexOf()

[Suisse00]

I was trying to create the definition for an addon of https://github.com/sequelize/sequelize 5.21.1 which would end up generating the sequelize definition as well.

the exception

Exception has occurred: TypeError
TypeError: Cannot read property 'indexOf' of undefined
at isNativeFunction (D:\Windows\Suisse\AppData\Roaming\npm\node_modules\dts-gen\bin\lib\index.js:358:25)
at getParameterListAndReturnType (D:\Windows\Suisse\AppData\Roaming\npm\node_modules\dts-gen\bin\lib\index.js:302:9)
at getResult (D:\Windows\Suisse\AppData\Roaming\npm\node_modules\dts-gen\bin\lib\index.js:135:30)
at getTopLevelDeclarations (D:\Windows\Suisse\AppData\Roaming\npm\node_modules\dts-gen\bin\lib\index.js:129:17)
at getResult (D:\Windows\Suisse\AppData\Roaming\npm\node_modules\dts-gen\bin\lib\index.js:197:35)
at getTopLevelDeclarations (D:\Windows\Suisse\AppData\Roaming\npm\node_modules\dts-gen\bin\lib\index.js:129:17)
at getResult (D:\Windows\Suisse\AppData\Roaming\npm\node_modules\dts-gen\bin\lib\index.js:153:17)
at getTopLevelDeclarations (D:\Windows\Suisse\AppData\Roaming\npm\node_modules\dts-gen\bin\lib\index.js:129:17)
at Object.generateIdentifierDeclarationFile (D:\Windows\Suisse\AppData\Roaming\npm\node_modules\dts-gen\bin\lib\index.js:73:20)
at Object. (D:\Windows\Suisse\AppData\Roaming\npm\node_modules\dts-gen\bin\lib\run.js:62:24)
at Module._compile (internal/modules/cjs/loader.js:685:14)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:699:10)
at Module.load (internal/modules/cjs/loader.js:598:32)
at tryModuleLoad (internal/modules/cjs/loader.js:537:12)
at Function.Module._load (internal/modules/cjs/loader.js:529:3)
at Function.Module.runMain (internal/modules/cjs/loader.js:741:12)
at startup (internal/bootstrap/node.js:285:19)
at bootstrapNodeJSCore (internal/bootstrap/node.js:739:3)

After investigating I found out the issue is when Proxy override the toString() method and return undefined.

Reproduction steps (from sequelize)

npm i -g sequelize
use my only changes from 5.21.1 - Suisse00/sequelize@eb1c7b1
dst-gen -m sequelize

Reproduction steps (POC)
poc.js
class Dummy {
static toString(...args) { return undefined; }
}

new Proxy(Dummy, {
get(target, p) {
return target[p];
}})

command

dts-gen --expression-file poc.js

dst-gen --version 0.5.8
sequelize 5.21.1 (with patch)

[Suisse00]

I did fix my errors by updating dts-gen, I have no idea if it will break something else but that could be a start.
Unfortunately, I updated the .js instead of the .ts, and I can't find the equivalent of Object.toString(X) in TS so... good luck!