MongoDB: javascript execution failed : can't save a DBQuery object at src/mongo/shell/collection.js

In MongoDb , when i try to modify existing document in collection , it generate the following exception : javascript execution failed : can't save a DBQuery object at src/mongo/shell/collection.js

In mongoDb shell i perform the following action :

 > var doc1 = db.users.find({name:"Harmeet"})
 > doc1.color = "Blue"
 > db.users.save(doc1)

when call to the save method the exception thow.