Benjamin Trent 181ee3ae0b
[ML] specifying missing_field_value value and using it instead of empty_string (#53108) (#53165)
For analytics, we need a consistent way of indicating when a value is missing. Inheriting from anomaly detection, analysis sent `""` when a field is missing. This works fine with numbers, but the underlying analytics process actually treats `""` as a category in categorical values. 

Consequently, you end up with this situation in the resulting model
```
{
              "frequency_encoding" : {
                "field" : "RainToday",
                "feature_name" : "RainToday_frequency",
                "frequency_map" : {
                  "" : 0.009844409027270245,
                  "No" : 0.6472019970785184,
                  "Yes" : 0.6472019970785184
                }
              }
            }
```
For inference this is a problem, because inference will treat missing values as `null`. And thus not include them on the infer call against the model.

This PR takes advantage of our new `missing_field_value` option and supplies `\0` as the value.
2020-03-05 09:50:52 -05:00
..
2020-03-04 16:17:55 +01:00