Handle cases where we get an empty key for an s:dict entry

[itay]

When EAI sends us s:dict entries (with nested s:key nodes), we parse
them as a dictionary in C#. However, it turns out the API can send us
a case where the value for the s:key node is actually the empty string,
which we do not expect and actually have a code contract to protect
against.

In that case, we will change it from the empty string to the string
called "empty" to be explicit about it. Since there can only be one
empty key per level (otherwise it would be a serious API error), this
is a reasonable workaround.

[itay]

An example bad XML snippet from the server:

      <s:key name="fieldMetadataStatic">
        <s:dict>
          <s:key name="">
            <s:dict>
              <s:key name="type">num</s:key>
            </s:dict>
          </s:key>
        </s:dict>
      </s:key>
      <s:key name="fieldMetadataEvents">
        <s:dict>
          <s:key name="">
            <s:dict>
              <s:key name="type">num</s:key>
            </s:dict>
          </s:key>
          <s:key name="EvaluatedField">
            <s:dict>
              <s:key name="type">num</s:key>
            </s:dict>
          </s:key>
        </s:dict>
      </s:key>
      <s:key name="fieldMetadataResults">
        <s:dict>
          <s:key name="">
            <s:dict>
              <s:key name="type">num</s:key>
            </s:dict>
          </s:key>
          <s:key name="EvaluatedField">
            <s:dict>
              <s:key name="type">num</s:key>
            </s:dict>
          </s:key>
        </s:dict>
      </s:key>

[David-Noble-at-work]

Looks good to me although I would prefer an alternative to "empty", perhaps "__empty" to minimize the risk of user-defined field name conflicts.

[itay]

FYI I will need to retarget this to develop. Will do it once all feedback is in.

[shakeelmohamed]

LGTM - I'd like to have a unit test in TestAtomFeed.cs that's basically the following (untested):

[Trait("unit-test", "Splunk.Client.AtomFeed")]
[Fact]
public async Task CanNormalizePropertyName()
{
    String goodName = AtomFeed.NormalizePropertyName("valid-name");
    Assert.Equal(result, "valid-name");
    String emptyName = AtomFeed.NormalizePropertyName("");
    Assert.Equal(emptyName, "empty");
}

edit: the empty string test can't be tested actually due to code contracts. We'll need to write tests around ParseDictionaryAsync

[glennblock]

Status here?

[shakeelmohamed]

Closed in favor of #60 against the develop branch