[{"car":"Honda","color":[null,null,null,null,null,null,null,null,null,"red","orange"]},{"car":"Toyota","color":[null,null,null,null,null,null,null,null,null,"red","orange"]},]

db.collection.update({color:{$exists:true,$eq:null}},[{$addFields:{color:{$filter:{input:"$color",as:"c",cond:{$ne:["$$c",null]}}}}}],{multi:true})