Update core API docs.

docs/development/core/server/kibana-plugin-core-server.md

@@ -270,6 +270,7 @@ The plugin integrates with the core system via lifecycle events: `setup`<!-- -->
 |  [SavedObjectsClientWrapperFactory](./kibana-plugin-core-server.savedobjectsclientwrapperfactory.md) | Describes the factory used to create instances of Saved Objects Client Wrappers. |
 |  [SavedObjectsFieldMapping](./kibana-plugin-core-server.savedobjectsfieldmapping.md) | Describe a [saved object type mapping](./kibana-plugin-core-server.savedobjectstypemappingdefinition.md) field.<!-- -->Please refer to [elasticsearch documentation](https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-types.html) For the mapping documentation |
 |  [SavedObjectsNamespaceType](./kibana-plugin-core-server.savedobjectsnamespacetype.md) | The namespace type dictates how a saved object can be interacted in relation to namespaces. Each type is mutually exclusive: \* single (default): this type of saved object is namespace-isolated, e.g., it exists in only one namespace. \* multiple: this type of saved object is shareable, e.g., it can exist in one or more namespaces. \* agnostic: this type of saved object is global.<!-- -->Note: do not write logic that uses this value directly; instead, use the appropriate accessors in the [type registry](./kibana-plugin-core-server.savedobjecttyperegistry.md)<!-- -->. |
+|  [SavedObjectUnsanitizedDoc](./kibana-plugin-core-server.savedobjectunsanitizeddoc.md) | We want to have two types, one that guarantees a "references" attribute will exist and one that allows it to be null. Since we're not migrating all the saved objects to have a "references" array, we need to support the scenarios where it may be missing (ex migrations). |
 |  [ScopeableRequest](./kibana-plugin-core-server.scopeablerequest.md) | A user credentials container. It accommodates the necessary auth credentials to impersonate the current user.<!-- -->See [KibanaRequest](./kibana-plugin-core-server.kibanarequest.md)<!-- -->. |
 |  [ServiceStatusLevel](./kibana-plugin-core-server.servicestatuslevel.md) | A convenience type that represents the union of each value in [ServiceStatusLevels](./kibana-plugin-core-server.servicestatuslevels.md)<!-- -->. |
 |  [SharedGlobalConfig](./kibana-plugin-core-server.sharedglobalconfig.md) |  |

docs/development/core/server/kibana-plugin-core-server.savedobjectscorefieldmapping.md

@@ -19,5 +19,6 @@ export interface SavedObjectsCoreFieldMapping
 |  [enabled](./kibana-plugin-core-server.savedobjectscorefieldmapping.enabled.md) | <code>boolean</code> |  |
 |  [fields](./kibana-plugin-core-server.savedobjectscorefieldmapping.fields.md) | <code>{</code><br/><code>        [subfield: string]: {</code><br/><code>            type: string;</code><br/><code>        };</code><br/><code>    }</code> |  |
 |  [index](./kibana-plugin-core-server.savedobjectscorefieldmapping.index.md) | <code>boolean</code> |  |
+|  [null\_value](./kibana-plugin-core-server.savedobjectscorefieldmapping.null_value.md) | <code>number &#124; boolean &#124; string</code> |  |
 |  [type](./kibana-plugin-core-server.savedobjectscorefieldmapping.type.md) | <code>string</code> |  |
 

docs/development/core/server/kibana-plugin-core-server.savedobjectscorefieldmapping.null_value.md

@@ -0,0 +1,11 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [SavedObjectsCoreFieldMapping](./kibana-plugin-core-server.savedobjectscorefieldmapping.md) &gt; [null\_value](./kibana-plugin-core-server.savedobjectscorefieldmapping.null_value.md)
+
+## SavedObjectsCoreFieldMapping.null\_value property
+
+<b>Signature:</b>
+
+```typescript
+null_value?: number | boolean | string;
+```

docs/development/core/server/kibana-plugin-core-server.savedobjectunsanitizeddoc.md

@@ -0,0 +1,13 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [SavedObjectUnsanitizedDoc](./kibana-plugin-core-server.savedobjectunsanitizeddoc.md)
+
+## SavedObjectUnsanitizedDoc type
+
+We want to have two types, one that guarantees a "references" attribute will exist and one that allows it to be null. Since we're not migrating all the saved objects to have a "references" array, we need to support the scenarios where it may be missing (ex migrations).
+
+<b>Signature:</b>
+
+```typescript
+export declare type SavedObjectUnsanitizedDoc = SavedObjectDoc & Partial<Referencable>;
+```

src/core/server/server.api.md

@@ -1840,6 +1840,8 @@ export interface SavedObjectsCoreFieldMapping {
     // (undocumented)
     index?: boolean;
     // (undocumented)
+    null_value?: number | boolean | string;
+    // (undocumented)
     type: string;
 }