How do I use dimension filters in Google Analytics API to omit records?

I'm using the Analytics reporting API to retrieve search terms, keywords, etc. I'd like to filter out instances where the search term is '(not set)' and have included what I thought were the appropriate dimension filters. However, the results that come back include records with the '(not set)' value in the search term field. I'm not sure what I'm missing and would appreciate any help. Thanks.

req =   {"reportRequests": [
            {"viewId": ACCOUNT,
            "dateRanges": [{"startDate": first, "endDate": last}],
            "metrics": [
                {"expression": "ga:impressions"},
                {"expression": "ga:adClicks"},
                {"expression": "ga:adCost"},
                {"expression": "ga:goalCompletionsAll"},
                {"expression": "ga:goalValueAll"},
                {"expression": "ga:transactions"},
                {"expression": "ga:transactionRevenue"},
                {"expression": "ga:sessions"}],
            "dimensions": [
                {"name": "ga:adMatchedQuery"},
                {"name": "ga:keyword"},
                {"name": "ga:adKeywordMatchType"},
                {"name": "ga:campaign"},
                {"name": "ga:adGroup"},
                {"name": "ga:date"},
                {"name": "ga:adwordsCampaignID"}],
            "dimensionFilterClauses": [
                {"operator": "OR",
                 "filters": [
                    {"dimensionName": "ga:adMatchedQuery",
                     "not": True,
                     "operator": "EXACT",
                     "expressions": ["(not set)"]},
                    {"dimensionName": "ga:keyword",
                     "not": True,
                     "operator": "IN_LIST",
                     "expressions": ["(not provided)", "(not set)"]}]}],
            "includeEmptyRows": "False",
            "pageSize": 100,
            "pageToken": nextpage,
            "hideTotals": True,
            "hideValueRanges": True}]}