Repro

{
    "rules": {
        "@typescript-eslint/no-unnecessary-condition": ["error"]
    }
}

function test(testVal?: boolean) {
    if (testVal ?? true) {
        console.log('test');
    }
}

Expected Result

No ESLint errors reported (condition inside the function is falsy only when we explicitly pass testVal = false).

Actual Result

2:20 error Unnecessary conditional, value is always truthy @typescript-eslint/no-unnecessary-condition

Additional info

I've noticed this recently when reading about additional options introduced in #1983, namely allowComparingNullableBooleansToFalse. With that option set to false, code like this:

function test(testVal?: boolean) {
    if (testVal !== false) {
        console.log('test');
    }
}

... turns into this with an autofix:

function test(testVal?: boolean) {
    if ((testVal ?? true)) {
        console.log('test');
    }
}

This is a valid transformation, since there should be only one situation when console.log() is run - when the testVal argument was explicitly set to false. Therefore, no-unnecessary-condition incorrectly reports that nullish coalescing is not needed here.

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