[{"_id":{"$oid":"62a3673660e2f16c7a7bc088"},"merchant":{"$oid":"62a3640560e2f16c7a7bc078"},"title":"24 Test 1","filter_conditions":{"city":["AAA","BBB","CCC","DDD"],"state":[],"pincode":["12345"]}},{"_id":{"$oid":"62a3673660e2f16c7a7bc089"},"merchant":{"$oid":"62a3640560e2f16c7a7bc079"},"title":"24 Test 2","filter_conditions":{"city":["AAA","BBB"]}}]

db.collection.aggregate([{$match:{$expr:{$cond:{if:{$ne:["$filter_conditions.pincode",undefined]},then:{$in:["12345",/** pincode value*/"$filter_conditions.pincode"]},else:{$cond:{if:{$ne:["$filter_conditions.city",undefined]},then:{$in:["AAA",/** city value*/"$filter_conditions.city"]},else:{$in:["",/** state value*/{$ifNull:["$filter_conditions.state",[]]}]}}}}}}}])