Major Description
We can get a decorrelation error because of rewrites that run in between DecorrelateInnerQuery and rewriteDomainJoins, that modify the correlation join conditions. In particular, ConstantFolding can transform `innercol <=> null` to `isnull(innercol)` and then rewriteDomainJoins does not recognize this and throws error Unable to rewrite domain join with conditions: ArrayBuffer(isnull(innercol#280)) because the isnull is not an equality, so it isn't usable for rewriting the domain join.
Can fix by recognizing `isnull(innercol)` as `innercol <=> null` in rewriteDomainJoins.
This area is also fragile in general and other rewrites that run between the two steps of decorrelation could potentially break their assumptions, so we may want to investigate longer-term follow ups for that.