Return friendly errors when bind variables are not set

[rkarthik007]

Running into an issue with the nodejs driver where one of the bind params was undefined.

Nodejs insert code:

    const insert = "INSERT INTO yb_ecommerce.products " +
                 "  (id, name, description, price, author, type, img, category)" +
                 " VALUES" +
                 "  (?, ?, ?, ?, ?, ?, ?, ?);"

    var insert_batch = [];
    // for loop here
    insert_batch.push({
      query: insert,
      params: params
    });

  client.batch(insert_batch, { prepare: true }, function(err) {
    ...
  });

The error I got back was:

E0308 21:28:51.414309 78086144 process_context.cc:180] SQL Error: Invalid Arguments. Runtime error (yb/yql/cql/cqlserver/cql_message.cc:131): Invalid bind variable kind -2
INSERT INTO yb_ecommerce.products   (id, name, description, price, author, type, img, category) VALUES  (?, ?, ?, ?, ?, ?, ?, ?);

@kmuthukk pointed out that in the code we do:

case Value::Kind::NOT_SET:
      break;
  }
  return STATUS_SUBSTITUTE(
      RuntimeError, "Invalid bind variable kind $0", static_cast<int>(v->kind));

where v->kind (an enum)'s value for NOT_SET is -2.

Rather than report the cryptic "-2", we should instead return a clear error and also indicate the bind position.

For example, for the NOT_SET case, we should instead return an error along the lines of:

   "No bind specified for bind position %d"