Remove "value" as required element of address_level (#283)

* Allow address_levels to be null

* Update doc

* Refactor to remove "value" as required element of address level container

* Update documentation description

* Fix missing null level

examples/addresses/address_all_missing_address_levels.yaml

@@ -0,0 +1,17 @@
+---
+id: overture:addresses:addres:1
+type: Feature
+geometry:
+  type: Point
+  coordinates: [-71.2086153, 42.3373725]
+properties:
+  theme: addresses
+  type: address
+  version: 0
+  country: US
+  address_levels:
+    - {}
+    - {}
+  postcode: '02459'
+  street: COMMONWEALTH AVE
+  number: '1000'

examples/addresses/address_missing_address_level.yaml

@@ -0,0 +1,17 @@
+---
+id: overture:addresses:addres:1
+type: Feature
+geometry:
+  type: Point
+  coordinates: [-71.2086153, 42.3373725]
+properties:
+  theme: addresses
+  type: address
+  version: 0
+  country: US
+  address_levels:
+    - value: MA
+    - {}
+  postcode: '02459'
+  street: COMMONWEALTH AVE
+  number: '1000'

schema/addresses/address.yaml

@@ -62,6 +62,11 @@ properties:     # JSON Schema: Top-level object properties.
           and the municipality. In other countries there might be only one.
           Other countries could have three or more. The array is ordered
           with the highest levels first.
+
+          Note: when a level is not known - most likely because the data provider
+          has not supplied it and we have not derived it from another source,
+          the array element container must be present, but the "value" field
+          should be omitted
         type: array
         items: { "$ref": "#/$defs/propertyContainers/addressLevelContainer" }
         minItems: 1
@@ -76,7 +81,6 @@ properties:     # JSON Schema: Top-level object properties.
         levels with per-country rules indicating which parts of a country's
         address goes to which numbered level.
       type: object
-      required: ["value"]
       properties:
         value:
           type: string