Type error agregate $cond

[giavy0209]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

6.4.1

Node.js version

any

MongoDB server version

any

Description

When I use $cond

 $cond: {
    if: {
      $in //throw type error here
    },
    then: POST_TYPE_DEFAULT.EVENT_TYPE.BIRTHDAY,
    else: POST_TYPE_DEFAULT.EVENT_TYPE.ANNIVERSARY
  }

I have read expression.d.ts, it's missing type ArrayExpressionOperatorReturningBoolean in type BooleanExpression

Steps to Reproduce

use Aggregate

model.aggregate([
  {
    $addFields : {
      $cond : {
         if : {$in : []} //throw type error here
       }
    }
  }
])

Expected Behavior

Can use $in in $cond.if