Name of affected component: Core Reporting API

Name of related library and version, if applicable (e.g. Java, Python,
HTTP, Objective-C, etc.): Whole API. We use Java lib "com.google.apis:google-api-services-analytics:v3-rev68-1.17.0-rc" but I tested it also at https://developers.google.com/oauthplayground/

Issue summary:
Hi,
I work in http://roihunter.com/ and these days we are trying to migrate our UTM format into new structure. We try to use utm_id query parameter as pairing parameter (previously we used to use utm_content), but we are missing some data from the API for entries without utm_id parameter. If some URL does not contain utm_id parameter data for this entry is not returned but I know there are some data in analytics.

Steps to reproduce issue:
1. Open playground at https://developers.google.com/oauthplayground/
2. Choose "Step 1: Select & authorize APIs" -> "Google Analytics API v3" -> https://www.googleapis.com/auth/analytics.readonly
3. Go to "Step 2: Exchange authorization code for tokens" and fill valid tokens.
4. Go to "Step 3: Configure request to API" and paste URL https://www.googleapis.com/analytics/v3/data/ga?ids=ga:85349312&start-date=2015-06-24&end-date=2015-06-24&dimensions=ga:date,ga:adContent,ga:campaignCode&metrics=ga:visitors,ga:transactions,ga:transactionRevenue&filters=ga:transactions>0;ga:adContent=~^at1![0-9]%2B$,ga:campaignCode=~^at1![0-9]%2B$

Expected output:
I expect the data with matching ga:adContent or matching ga:campaignCode is returned.

Actual results:
Only data with matching ga:campaignCode is returned - the old data without ga:campaignCode (utm_id  in URL) is missing.

Notes:
I would expect, that for missing ga:campaignCode there is some value "(not set)" like for ga:adContent so merge of old and new data is returned.