aprimadi commented on issue #6179:
URL: 
https://github.com/apache/arrow-datafusion/issues/6179#issuecomment-1537199622

   CMIIW. I may miss something here.
   
   It looks like we can just propagate the type information top-down from 
overall expressions to subexpression. Let's just say for the purpose of this 
issue we only have two types: `BoolType` and `NullType`. In a filter, the 
simplifier walks the subtree starting from `BoolType`, only changing it's type 
to `NullType` if it encounters these two statements:
   
   ```
   (...) IS NULL
   (...) IS NOT NULL
   ```
   
   Once a type changed to `NullType`, it can't be changed back to `BoolType` in 
subexpressions.


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