Application of mqlread cursor leads to non-unique error - freebase

Question

This is a freebase mqlread query to get some id's about each film.
https://www.googleapis.com/freebase/v1/mqlread?query=[{ "name": null, "mid": null, "type": "/film/film", "/film/film/rottentomatoes_id": null, "/film/film/imdb_id": null }]&cursor
That works and returns this cursor.
=eNpVjMEKwjAQRH9HkdDZsNlNFhH_I_QQYgsFsdKgR7_dIII4lxlmmFcfW1s3oyKT5dUIGPOtm3pETiGMSysG9y1U2a5Ht3sudyMNGgXxtwXbDsnDl1jBAIRpjvhTdafPD6L7gRI6gezlcus8yDicRaYLMc9Qrkm5x8B4A72MKIs=
My problem is the subsequent call formulated by appending the cursor value which does not work. See below.
https://www.googleapis.com/freebase/v1/mqlread?query=[{ "name": null, "mid": null, "type": "/film/film", "/film/film/rottentomatoes_id": null, "/film/film/imdb_id": null }]&cursor=eNpVjMEKwjAQRH9HkdDZsNlNFhH_I_QQYgsFsdKgR7_dIII4lxlmmFcfW1s3oyKT5dUIGPOtm3pETiGMSysG9y1U2a5Ht3sudyMNGgXxtwXbDsnDl1jBAIRpjvhTdafPD6L7gRI6gezlcus8yDicRaYLMc9Qrkm5x8B4A72MKIs=
This gives
{
"error": {
"errors": [
{
"domain": "global",
"reason": "invalid",
"message": "query is invalid: JSON parsing error.",
"locationType": "other",
"location": "parameters.query"
}
],
"code": 400,
"message": "query is invalid: JSON parsing error."
}
}
but all thats changed is the appendage of the cursor value.
Why would I get this sort of error in the circumstance and how would I fix it.

Answer 1

Some of your properties aren't unique. If you get only one value back, the query will work fine, but as soon as you hit a topic with multiple values, you'll get a non-unique error like this:
error: {
errors: [
{
domain: "global",
reason: "invalid",
message: "Unique query may have at most one result. Got 2",
locationType: "other",
location: "/film/film/rottentomatoes_id"
}
],
code: 400,
message: "Unique query may have at most one result. Got 2"
}
The error message is pretty specific. The offending property is the one for Rotten Tomatoes ID. If you switch your placeholder value from "null" to [] for this property to accommodate multiple values, the query will work.