title: concat Jolt transformation works on demo site; does not work in code
body: <p>I'd like to concatenate a couple of fields using Jolt (<code>com.bazaarvoice.jolt:jolt-core:0.1.1</code> and <code>com.bazaarvoice.jolt:json-utils:0.1.1</code>). Here's an example input record:</p>
  
  <pre><code>{
    "ts": 1572873208.555711,
    "uid": "CQXg712bv3ayjojRwd",
    "orig_lat": 39.997,
    "orig_long": -105.0974,
    "resp_lat": 39.0481,
    "resp_long": -77.4728
  }
  </code></pre>
  
  <p>... and this is the Jolt transformation:</p>
  
  <pre><code>[
    {
      "operation": "modify-default-beta",
      "spec": {
        "orig_location": "=concat(@(1,orig_lat),',',@(1,orig_long))",
        "resp_location": "=concat(@(1,resp_lat),',',@(1,resp_long))"
      }
    }
  ]
  </code></pre>
  
  <p>... and this is the output of the transformation from the <a href="https://jolt-demo.appspot.com/" rel="nofollow noreferrer">Jolt Transform Demo site</a>:</p>
  
  <pre><code>{
    "ts" : 1.572873208555711E9,
    "uid" : "CQXg712bv3ayjojRwd",
    "orig_lat" : 39.997,
    "orig_long" : -105.0974,
    "resp_lat" : 39.0481,
    "resp_long" : -77.4728,
    "orig_location" : "39.997,-105.0974",
    "resp_location" : "39.0481,-77.4728"
  }
  </code></pre>
  
  <p>I tried to do this programatically:</p>
  
  <pre><code>String input = "{\"ts\":1572873208.555711,\"uid\":\"CQXg712bv3ayjojRwd\",\"orig_lat\":39.997,\"orig_long\":-105.0974,\"resp_lat\":39.0481,\"resp_long\":-77.4728}";
  
  String JOLT_SPEC_LIST = "[\n" +
          "  {\n" +
          "    \"operation\": \"modify-default-beta\",\n" +
          "    \"spec\": {\n" +
          "      \"orig_location\": \"=concat(@(1,orig_lat),',',@(1,orig_long))\",\n" +
          "      \"resp_location\": \"=concat(@(1,resp_lat),',',@(1,resp_long))\"\n" +
          "    }\n" +
          "  }\n" +
          "]";
  
  Chainr chainr = Chainr.fromSpec(JsonUtils.jsonToList(JOLT_SPEC_LIST));
  Object transformed = chainr.transform(input);
  </code></pre>
  
  <p>The <code>transformed</code> object is supposed to contain the transformed output. For some reason, the output is identical to the input. It does not contain the two derived fields.</p>
  
  <p>Can you see what I'm doing wrong?</p>