Thanks for the PR,@yeonjuan!

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Codecov Report

Merging#2111 intomaster willincrease coverage by0.00%.
The diff coverage is100.00%.

@@           Coverage Diff           @@##           master    #2111   +/-   ##=======================================  Coverage   93.42%   93.42%           =======================================  Files         171      171             Lines        7755     7757    +2       Branches     2215     2216    +1     =======================================+ Hits         7245     7247    +2  Misses        244      244             Partials      266      266

Unless I'm mistaken, I believe this is addressing#1977. If I'm right, please add it to the OP 😄

@bradzacher
Well, I found this issue while trying to solve#1977, but it's quite a different issue.
#1977 occurs when a node's nullable type is originated from its parent nullable, but this issue occurs when theOptionalMemberExpression's last member is nullable type. (In my thought)

so this pr can't fix#1977

letx:{a:{b:string}}|null;x?.a?.b;^^// a's nullable type is originated from x's type, so this case belong #1977letx:{a?:string};x?.a;// no error^^// IMO, we should check type of "x" not "a"