Custom YQL table for Tumblr likes - json

Question

I'm trying to make a custom YQL table to access a user's likes through the Tumblr API. I made the following table in the YQL editor and saved it as tumblr.likes:
<?xml version="1.0" encoding="UTF-8"?>
<table xmlns="http://query.yahooapis.com/v1/schema/table.xsd">
<meta>
<author>nonphoto</author>
<documentationURL>http://www.tumblr.com/docs/api</documentationURL>
<sampleQuery>select * from {table} where username='XXX' api_key='XXX'</sampleQuery>
</meta>
<bindings>
<select itemPath="response.liked_posts" produces="JSON">
<urls>
<url>http://api.tumblr.com/v2/blog/{username}.tumblr.com/likes</url>
</urls>
<inputs>
<key id="username" type="xs:string" paramType="path" required="true" />
<key id="api_key" type="xs:string" paramType="query" required="true" />
</inputs>
</select>
</bindings>
</table>
If this is correct then I should be able to type this query into the YQL console and get a JSON response back from Tumblr:
use "XXX" as tumblr.likes;
select * from tumblr.likes where username='XXX' and api_key='XXX';
But null appears in the results entry of the response, even if debug and diagnostics are checked to prevent caching. The response even shows the correct URL, which works if I just copy and paste it into my browser. Am I missing something? Here's an example response:
{
"query": {
"count": 0,
"created": "2016-01-15T21:44:36Z",
"lang": "en-US",
"diagnostics": {
"url": [
{
"execution-start-time": "2",
"execution-stop-time": "8",
"execution-time": "6",
"id": "579e13ad-a7c3-4eea-81d9-41fda5caf243",
"content": "http://sherpa-bcp5903.dht.yahoo.com:4080/YDHTWebService/V1/get/yql.global/store%3A%2F%2FoSSGByQMlFLQhMqNCwUcp1"
},
{
"execution-start-time": "14",
"execution-stop-time": "1137",
"execution-time": "1123",
"id": "ffab25db-521f-4795-9220-a82e2ac33a9d",
"content": "http://api.tumblr.com/v2/blog/XXX.tumblr.com/likes?api_key=XXX"
}
],
"publiclyCallable": "true",
"user-time": "1146",
"service-time": "1129",
"build-version": "0.2.942"
},
"results": null
}
}