Switch on strictNullChecks and fix all issues

[ibeckermayer]

See: https://www.typescriptlang.org/tsconfig/#strictNullChecks

[hatched]

I think we can take this one step further and work towards enabling strict. Doing so creates 1650 errors, 888 of which are strictNullChecks.

[ravicious]

Some posts about performing a gradual migration that I found:

• https://kevinwil.de/incremental-migration/
• https://code.visualstudio.com/blogs/2019/05/23/strict-null

[JanKaczmarkiewicz]

If we don't have circular dependencies between packages (package A installs package B and package B installs package A) we could use https://www.typescriptlang.org/docs/handbook/project-references.html

This way each package will have a separate tsconfig, so each package is compiled with different options so we can adopt strict mode package after package and option after option. Also, IDE understands that: we get errors from strict options only in enabled packages.

We used this approach (in prev company) some time ago to adopt a gradually strict mode big in monorepo project (~270k lines of code, 15 packages)

I could prepare the PoC branch if you want.

resources:

• simple example https://github.com/RyanCavanaugh/project-references-demo
• real world example https://github.com/facebook/jest/tree/main/packages
• cyclic deps discussion Allow circular references of project references microsoft/TypeScript#33685
• docs https://www.typescriptlang.org/docs/handbook/project-references.html