diff --git a/packages/ra-core/src/auth/useGetIdentity.ts b/packages/ra-core/src/auth/useGetIdentity.ts
index 667f7727487..0361c8c218b 100644
--- a/packages/ra-core/src/auth/useGetIdentity.ts
+++ b/packages/ra-core/src/auth/useGetIdentity.ts
@@ -4,9 +4,8 @@ import { useQuery, UseQueryOptions, QueryObserverResult } from 'react-query';
 import useAuthProvider from './useAuthProvider';
 import { UserIdentity } from '../types';
 
-const defaultIdentity = {
+const defaultIdentity: UserIdentity = {
     id: '',
-    fullName: null,
 };
 const defaultQueryParams = {
     staleTime: 5 * 60 * 1000,
@@ -48,9 +47,18 @@ export const useGetIdentity = (
 
     const result = useQuery(
         ['auth', 'getIdentity'],
-        authProvider
-            ? () => authProvider.getIdentity()
-            : async () => defaultIdentity,
+        async () => {
+            if (
+                authProvider &&
+                typeof authProvider.getIdentity === 'function'
+            ) {
+                const identity = await authProvider.getIdentity();
+                return identity || defaultIdentity;
+            } else {
+                return defaultIdentity;
+            }
+        },
+
         {
             enabled: typeof authProvider?.getIdentity === 'function',
             ...queryParams,
@@ -64,18 +72,29 @@ export const useGetIdentity = (
                 ? { isLoading: true }
                 : result.error
                 ? { error: result.error, isLoading: false }
-                : {
+                : result.isSuccess
+                ? {
                       data: result.data,
                       identity: result.data,
                       refetch: result.refetch,
                       isLoading: false,
-                  },
+                  }
+                : { isLoading: false },
 
         [result]
     );
 };
 
 export type UseGetIdentityResult =
+    // idle result
+    | {
+          isLoading: false;
+          data?: undefined;
+          identity?: undefined;
+          error?: undefined;
+          refetch?: undefined;
+      }
+    // loading result
     | {
           isLoading: true;
           data?: undefined;
@@ -83,6 +102,7 @@ export type UseGetIdentityResult =
           error?: undefined;
           refetch?: undefined;
       }
+    // error result
     | {
           isLoading: false;
           data?: undefined;
@@ -90,6 +110,7 @@ export type UseGetIdentityResult =
           error: Error;
           refetch?: undefined;
       }
+    // success result
     | {
           isLoading: false;
           data: UserIdentity;
diff --git a/packages/ra-core/src/auth/useHandleAuthCallback.ts b/packages/ra-core/src/auth/useHandleAuthCallback.ts
index a4af2bcd3ab..2941a88a785 100644
--- a/packages/ra-core/src/auth/useHandleAuthCallback.ts
+++ b/packages/ra-core/src/auth/useHandleAuthCallback.ts
@@ -1,7 +1,7 @@
 import { useQuery, UseQueryOptions } from 'react-query';
 import { useLocation } from 'react-router';
 import { useRedirect } from '../routing';
-import { AuthProvider, AuthRedirectResult } from '../types';
+import { AuthRedirectResult } from '../types';
 import useAuthProvider from './useAuthProvider';
 
 /**
@@ -12,7 +12,7 @@ import useAuthProvider from './useAuthProvider';
  * @returns An object containing { isLoading, data, error, refetch }.
  */
 export const useHandleAuthCallback = (
-    options?: UseQueryOptions<ReturnType<AuthProvider['handleCallback']>>
+    options?: UseQueryOptions<AuthRedirectResult | void | any>
 ) => {
     const authProvider = useAuthProvider();
     const redirect = useRedirect();
@@ -24,7 +24,10 @@ export const useHandleAuthCallback = (
 
     return useQuery(
         ['auth', 'handleCallback'],
-        () => authProvider.handleCallback(),
+        () =>
+            authProvider && typeof authProvider.handleCallback === 'function'
+                ? authProvider.handleCallback()
+                : Promise.resolve(),
         {
             retry: false,
             onSuccess: data => {
diff --git a/packages/ra-core/src/core/useResourceDefinitions.ts b/packages/ra-core/src/core/useResourceDefinitions.ts
index c7c8c2d46dc..9846703fc72 100644
--- a/packages/ra-core/src/core/useResourceDefinitions.ts
+++ b/packages/ra-core/src/core/useResourceDefinitions.ts
@@ -1,4 +1,5 @@
-import { ResourceDefinitions } from './ResourceDefinitionContext';
+import type { ResourceOptions } from '../types';
+import type { ResourceDefinitions } from './ResourceDefinitionContext';
 import { useResourceDefinitionContext } from './useResourceDefinitionContext';
 
 /**
@@ -20,6 +21,6 @@ import { useResourceDefinitionContext } from './useResourceDefinitionContext';
  * // }
  */
 export const useResourceDefinitions = <
-    OptionsType = any
+    OptionsType extends ResourceOptions = any
 >(): ResourceDefinitions<OptionsType> =>
     useResourceDefinitionContext().definitions;
diff --git a/packages/ra-core/src/dataProvider/fetch.ts b/packages/ra-core/src/dataProvider/fetch.ts
index 9a7c7b47466..9bd5cb74708 100644
--- a/packages/ra-core/src/dataProvider/fetch.ts
+++ b/packages/ra-core/src/dataProvider/fetch.ts
@@ -95,7 +95,7 @@ const isValidObject = value => {
     return !isArray && !isBuffer && isObject && hasKeys;
 };
 
-export const flattenObject = (value, path = []) => {
+export const flattenObject = (value: any, path: string[] = []) => {
     if (isValidObject(value)) {
         return Object.assign(
             {},
diff --git a/packages/ra-core/src/form/useUnique.ts b/packages/ra-core/src/form/useUnique.ts
index 221a41c3059..e48ec5ac1ca 100644
--- a/packages/ra-core/src/form/useUnique.ts
+++ b/packages/ra-core/src/form/useUnique.ts
@@ -106,7 +106,11 @@ export const useUnique = (options?: UseUniqueOptions) => {
                         }
                     );
 
-                    if (total > 0 && !data.some(r => r.id === record?.id)) {
+                    if (
+                        typeof total !== 'undefined' &&
+                        total > 0 &&
+                        !data.some(r => r.id === record?.id)
+                    ) {
                         return {
                             message,
                             args: {