Mongo $and/$or/$nor array items should be validated as objects

[simonbrunel]

MongoDB $and, $nor and $or operators expect array of expressions (i.e. objects):

{ $and: [ { <expression1> }, { <expression2> } , ... , { <expressionN> } ] }
{ $nor: [ { <expression1> }, { <expression2> }, ...  { <expressionN> } ] }
{ $or: [ { <expression1> }, { <expression2> }, ... , { <expressionN> } ] }

However, it seems that the ucast/mongo parser doesn't validate these entries, thus it's possible to call:

parse({ $and: ["foo", 42] })  // e.g. from received HTTP query

No exception thrown but the following condition returned:

{
  "operator": "and",
  "value": [
    {
      "operator": "eq",
      "value": "f",
      "field": "0"
    },
    {
      "operator": "eq",
      "value": "o",
      "field": "1"
    },
    {
      "operator": "eq",
      "value": "o",
      "field": "2"
    }
  ]
}

42 seems to be ignored in this case, probably because Object.keys(42) returns [].

Instead, we should expect an error like Error('"$and" expects value to be an array of objects');

Same applies to calling parse("foo") directly with a non object value, which should be prevented by type checking (i.e. parse expects a record) but can still happen if the value is any. Though I'm not sure if it should be handled by the lib or explicitly by the user, which should make sure to pass an object to parse.