Fixes the null pointer exception

Issue #42
Bug fixes and general Field class done.

Finally fixed the tomcat issues:
fixes #42
fixes #41 - Added sessionid, local servername to output

Completed most of #26, just need to add metrics and
Ocado team specific classes.

{
    "message": "GET /etoheubtoe?teethiae=rc,.dudx,.u HTTP/1.1 404",
    "tags": [
        "tag1",
        "tag2",
        "tag3",
        "valve"
    ],
    "@timestamp": "2013-10-24T20:23:46.222Z",
    "field3": "value3",
    "field2": "value2",
    "level": "ERROR",
    "http": {
        "request_protocol": "HTTP/1.1",
        "response_headers": {},
        "request_querystring": "teethiae=rc,.dudx,.u",
        "remote_user": null,
        "request_headers": {
            "Referer": null,
            "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/30.0.1599.101 Safari/537.36"
        },
        "response_size": 985,
        "response_status": 404,
        "request_parameters": {
            "teethiae": [
                "rc,.dudx,.u"
            ]
        },
        "request_uri": "/etoheubtoe",
        "remote_host": "192.168.1.208",
        "server_name": "192.168.1.67",
        "request_method": "GET",
        "response_duration": 27,
        "cookies": {}
    },
    "hostname": "precise64",
    "field1": "value1",
    "@version": "1",
    "user": "tomcat7"
}