feat(lint): created local rule to use isNullish and nonNullish

[AntonioVentilii-DFINITY]

Motivation

We would like to enforce the usage of functions isNullish and nonNullish in the code whenever possible. As first step we look for instances of comparing a variable with undefined and/or null.

isNullish

Incorrect

param === undefined

param === null

param === undefined || param === null

Correct

isNullish(param);

nonNullish

Incorrect

param !== undefined

param !== null

param !== null && param !== undefined

Correct

nonNullish(param);

Future Improvements

The rule will be improved to recognize nullish check even with the following cases (and their negation counterparty):

const param: NonBooleanType | undefined | null;

if (param) {...}

param ? ... : ...

param && ...

param || ...

Note

In this PR, we will not solve all the new issues raised by the new rule, otherwise it would become too big: we add the exceptions to the rule with a TODO, for all the functions that we need to fix in other PRs.

Changes

• Created custom local lint rule for isNullish usage.
• Created custom local lint rule for nonNullish usage.
• Create exceptions where necessary.
• Fix issues created by new rules related to .find function.
• Add temporary exceptions to the rule with a TODO associated.

Tests

It raised issues, correctly, and we fixed it.

[AntonioVentilii-DFINITY]

After PR #2552 , I am moving the rule definition to the https://github.com/dfinity/eslint-config-oisy-wallet repo and the change this PR to be just the adaptation to the new rule.

Working on it with PR:

• feat: enforce usage of nullish check utils eslint-config-oisy-wallet#12