use test
db.data.remove()
db.data.insert(

{position:[1,1]}

)
db.data.ensureIndex(

{position:'2d'}

)

db.data.find({position:{$near:[1,1]}})
// -> ok

db.data.find({position:{$near:[1,1]}}).limit(1)
// -> error:

{ "$err" : "assertion db/geo/2d.cpp:290" }

db.runCommand (

{ geoNear : "data" , near : [1,1], num : 2}

);
// -> ok

db.runCommand (

{ geoNear : "data" , near : [1,1], num : 1}

);
// -> "errmsg" : "exception: assertion db/geo/2d.cpp:290",