title: Can't create Druid ingestion task through API
body: <p>When I send JSON ingestion specification to Druid overlord API I get this response: </p>
  
  <pre><code>HTTP/1.1 400 Bad Request
  Content-Type: application/json
  Date: Wed, 25 Sep 2019 11:44:18 GMT
  Server: Jetty(9.4.10.v20180503)
  Transfer-Encoding: chunked
  
  {
      "error": "Instantiation of [simple type, class org.apache.druid.indexing.common.task.IndexTask] value failed: null"
  }
  </code></pre>
  
  <p>If I change <code>index</code> task type to <code>index_parallel</code>, then I get this: </p>
  
  <pre><code>{
      "error": "Instantiation of [simple type, class org.apache.druid.indexing.common.task.batch.parallel.ParallelIndexSupervisorTask] value failed: null"
  }
  </code></pre>
  
  <p><strong>Using same ingestion spec through Druid's web UI works fine.</strong></p>
  
  <p>Here is the ingestion spec that I use(slightly modified to hide sensitive data):</p>
  
  <pre><code>{
      "type": "index_parallel",
      "dataSchema": {
        "dataSource": "daily_xport_test",
        "granularitySpec": {
          "type": "uniform",
          "segmentGranularity": "MONTH",
          "queryGranularity": "NONE",
          "rollup": false
        },
        "parser": {
          "type": "string",
          "parseSpec": {
            "format": "json",
            "timestampSpec": {
              "column": "dateday",
              "format": "auto"
            },
            "dimensionsSpec": {
              "dimensions": [
                {
                  "type": "string",
                  "name": "id",
                  "createBitmapIndex": true
                },
                {
                  "type": "long",
                  "name": "clicks_count_total"
                },
                {
                  "type": "long",
                  "name": "ctr"
                },
                "deleted",
                "device_type",
                "target_url"
              ]
            }
          }
        }
      },
      "ioConfig": {
        "type": "index_parallel",
        "firehose": {
          "type": "static-google-blobstore",
          "blobs": [
            {
              "bucket": "data-test",
              "path": "/sample_data/daily_export_18092019/000000000000.json.gz"
            }
          ],
          "filter": "*.json.gz$"
        },
        "appendToExisting": false
      },
      "tuningConfig": {
        "type": "index_parallel",
        "maxNumSubTasks": 1,
        "maxRowsInMemory": 1000000,
        "pushTimeout": 0,
        "maxRetry": 3,
        "taskStatusCheckPeriodMs": 1000,
        "chatHandlerTimeout": "PT10S",
        "chatHandlerNumRetries": 5
      }
    }
  
  </code></pre>
  
  <p>Overlord API URI looks like this:</p>
  
  <pre><code>http://host:8081/druid/indexer/v1/task
  </code></pre>
  
  <p>HTTPie command to send API request:</p>
  
  <pre class="lang-sh prettyprint-override"><code>http --print=Hhb  POST http://host:8081/druid/indexer/v1/task &lt; test_spec.json
  </code></pre>
  
  <p><strong>Also, I get the same issue if I try to send ingestion task using DruidHook class in Airflow</strong></p>