ReactStylesDiffMap

Wrapper for ReadableMap which should be used for styles property map. It extends some of the accessor methods of ReadableMap by adding a default value property such that caller is enforced to provide a default value for a style property.

Instances of this class are used to update View or CSSNode style properties. Since properties are generated by React framework based on what has been updated each value in this map should either be interpreted as a new value set for a style property or as a "reset this property to default" command in case when value is null (this is a way React communicates change in which the style key that was previously present in a map has been removed).

NOTE: Accessor method with default value will throw an exception when the key is not present in the map. Style applicator logic should verify whether the key exists in the map using hasKey before fetching the value. The motivation behind this is that in case when the updated style diff map doesn't contain a certain style key it means that the corresponding view property shouldn't be updated (whereas in all other cases it should be updated to the new value or the property should be reset).