Allow Null Date Values

[ndickerson]

Date values start out as null (no value). Once a date value is set, it can never be unset back to null.

The current implementation of the object mapper ignores all null values, including date values, and only a null value can set the date back to it's original empty state. The proper JSON payload for setting a null date value is:

{
    "customDate1": null
}

This is not currently achievable with the global Jackson annotation:

@JsonInclude(JsonInclude.Include.NON_NULL)

Which is used in order to avoid race conditions that occur when sending all values, including null values that were not set on the entity object. In order to support the sending of null values for dates, there will have to be special logic that determines when a user has explicitly set a null value on the date, and distinguish that from the initial default state of the object.

[ndickerson]

De-prioritizing this issue since it would require a major rewrite at this point for only a small added benefit.