Change fog and terrain types to match Mapbox types. (#2106)

Author: fpsampayo

docs/api-reference/map.md

@@ -73,10 +73,10 @@ The current cursor [type](https://developer.mozilla.org/en-US/docs/Web/CSS/curso
 
 ### Styling options
 
-#### `fog`: [Fog](/docs/api-reference/types.md#fog) | null
+#### `fog`: [Fog](/docs/api-reference/types.md#fog)
 
 The fog property of the style. Must conform to the [Fog Style Specification](https://docs.mapbox.com/mapbox-gl-js/style-spec/fog/).
-If `null` is provided, removes the fog from the map.
+If `undefined` is provided, removes the fog from the map.
 
 #### `light`: [Light](/docs/api-reference/types.md#light)
 
@@ -109,7 +109,7 @@ Enable diffing when `mapStyle` changes. If `false`, force a 'full' update, remov
 #### `terrain`: [TerrainSpecification](/docs/api-reference/types.md#terrainspecification)
 
 Terrain property of the style. Must conform to the [Terrain Style Specification](https://docs.mapbox.com/mapbox-gl-js/style-spec/terrain/).
-If `null` is provided, removes terrain from the map.
+If `undefined` is provided, removes terrain from the map.
 
 
 ### Camera options

src/mapbox/mapbox.ts

@@ -257,13 +257,13 @@ export type MapboxProps = Partial<ViewState> & {
    */
   styleDiffing?: boolean;
   /** The fog property of the style. Must conform to the Fog Style Specification .
-   * If `null` is provided, removes the fog from the map. */
-  fog?: Fog | null;
+   * If `undefined` is provided, removes the fog from the map. */
+  fog?: Fog;
   /** Light properties of the map. */
   light?: Light;
   /** Terrain property of the style. Must conform to the Terrain Style Specification .
-   * If `null` is provided, removes terrain from the map. */
-  terrain?: TerrainSpecification | null;
+   * If `undefined` is provided, removes terrain from the map. */
+  terrain?: TerrainSpecification;
   /** Default layers to query on pointer events */
   interactiveLayerIds?: string[];
   /** The projection the map should be rendered in

test/src/utils/mapbox-gl-mock/style.js

@@ -11,8 +11,8 @@ export default class Style {
 
     this._loaded = false;
     this._light = null;
-    this._fog = null;
-    this._terrain = null;
+    this._fog = undefined;
+    this._terrain = undefined;
 
     this._sources = {};
     this._layers = [];