Some special cases of index interval bounds are created from operators, such as $type and $exists. The base transformation of intervals to match expressions in SERVER-104501 in these cases would create comparison expressions. 

Check if this transformation is sufficient from the performance and accuracy perspective.

If not, add specific transformation rules.

The specific match expressions are:

• $type -> [minVal, maxVal]
• {$exists : false} -> [null, null]
• internal comparison expressions