Investigate handling of null values in ValueTypeRepresenter

[markpollack]

currenlty writing null values of the form

  "applicationProperties": !!null "null"
  "deploymentProperties": !!null "null"

Do we want this format? How does it relate to handling of null values for a given key in the map and that indicating to 'remove' a property when upgrading a relrease.

[tzolov]

Some related docs:

• YAML tags and Java types - Note: not sure how SnakeYAML specific is this.
• YAML 1.1 Tags