String filters and Null values

[kzangeli]

The string filters don't consider attribute/metadata values of type Null.
For some reason this case wasn't taken into consideration when implementing the string filters.

Effort: 1 man day

[fgalan]

To be precise, this issue refers to the JSON datatype null.

[fgalan]

Both for q and mq.

[kzangeli]

We might have just forgotten about NULL when implementing string filters.
However, I did a quick test and it failed:

StringFilter::mongoFilterPopulate()
{
  ...
  case SfvtNull:
    bb.append("$exists", true).append("$in", BSON_ARRAY("null"));
    break;

That try gives the string "null" in the query:

attrs.A1.value.N: { $exists: true, $in: [ "null" ] } }

And trying with NULL:

  case SfvtNull:
    bb.append("$exists", true).append("$in", BSON_ARRAY(NULL));
    break;

Well, that doesn't even compile.
Not very important, leaving it for later.
To fix this, look at servicePath and copy how it's done there:

servicePath: { $in: [ /^/.*/, null ] }

[fgalan]

Not sure, but I remember something like this in a similar case... it may work.

    BSONObj empty;
    bb.append("$exists", true).append("$in", BSON_ARRAY(empty));

[fgalan]

Fixed by PR #2806