diff --git a/packages/ra-core/src/form/FormDataConsumer.tsx b/packages/ra-core/src/form/FormDataConsumer.tsx
index bbb4a82598e..519e3ea80ce 100644
--- a/packages/ra-core/src/form/FormDataConsumer.tsx
+++ b/packages/ra-core/src/form/FormDataConsumer.tsx
@@ -56,7 +56,7 @@ export const FormDataConsumerView = (props: Props) => {
     let ret;
 
     // If we have an index, we are in an iterator like component (such as the SimpleFormIterator)
-    if (typeof index !== 'undefined') {
+    if (typeof index !== 'undefined' && source) {
         scopedFormData = get(formData, source);
         getSource = (scopedSource: string) => {
             getSourceHasBeenCalled = true;
diff --git a/packages/ra-core/src/form/FormGroupsContext.tsx b/packages/ra-core/src/form/FormGroupsContext.tsx
index d01af9d7274..5a1f3cc9a8d 100644
--- a/packages/ra-core/src/form/FormGroupsContext.tsx
+++ b/packages/ra-core/src/form/FormGroupsContext.tsx
@@ -1,8 +1,8 @@
 import { createContext } from 'react';
 
-export const FormGroupsContext = createContext<FormGroupsContextValue>(
-    undefined
-);
+export const FormGroupsContext = createContext<
+    FormGroupsContextValue | undefined
+>(undefined);
 
 export type FormGroupSubscriber = () => void;
 
diff --git a/packages/ra-core/src/form/choices/ChoicesContext.ts b/packages/ra-core/src/form/choices/ChoicesContext.ts
index f7a42996080..3421d93bba5 100644
--- a/packages/ra-core/src/form/choices/ChoicesContext.ts
+++ b/packages/ra-core/src/form/choices/ChoicesContext.ts
@@ -6,7 +6,9 @@ import { FilterPayload, RaRecord, SortPayload } from '../../types';
  *
  * Use the useChoicesContext() hook to read the context.
  */
-export const ChoicesContext = createContext<ChoicesContextValue>(undefined);
+export const ChoicesContext = createContext<ChoicesContextValue | undefined>(
+    undefined
+);
 
 export type ChoicesContextValue<RecordType extends RaRecord = any> = {
     allChoices: RecordType[];
diff --git a/packages/ra-core/src/form/getFormInitialValues.ts b/packages/ra-core/src/form/getFormInitialValues.ts
index 565899792a1..a6ae3121a05 100644
--- a/packages/ra-core/src/form/getFormInitialValues.ts
+++ b/packages/ra-core/src/form/getFormInitialValues.ts
@@ -3,7 +3,7 @@ import { RaRecord } from '../types';
 
 export default function getFormInitialValues(
     defaultValues: DefaultValue,
-    record: Partial<RaRecord>
+    record?: Partial<RaRecord>
 ) {
     const finalInitialValues = merge(
         {},
diff --git a/packages/ra-core/src/form/getSimpleValidationResolver.ts b/packages/ra-core/src/form/getSimpleValidationResolver.ts
index 3dfab345e05..4cf693fd5c5 100644
--- a/packages/ra-core/src/form/getSimpleValidationResolver.ts
+++ b/packages/ra-core/src/form/getSimpleValidationResolver.ts
@@ -4,7 +4,7 @@ import { ValidationErrorMessageWithArgs } from './validate';
 
 // Flattening an object into path keys:
 // https://github.com/lodash/lodash/issues/2240#issuecomment-418820848
-export const flattenErrors = (obj, path = []) =>
+export const flattenErrors = (obj, path: string[] = []) =>
     !_.isObject(obj)
         ? { [path.join('.')]: obj }
         : _.reduce(
diff --git a/packages/ra-core/src/form/setSubmissionErrors.ts b/packages/ra-core/src/form/setSubmissionErrors.ts
index c21d38356b3..155c8a0962c 100644
--- a/packages/ra-core/src/form/setSubmissionErrors.ts
+++ b/packages/ra-core/src/form/setSubmissionErrors.ts
@@ -39,7 +39,7 @@ export const setSubmissionErrors = (
             });
         });
     };
-    const setErrorFromObject = (errors: any, rootPath: string) => {
+    const setErrorFromObject = (errors: FieldValues, rootPath: string) => {
         Object.entries(errors).forEach(([name, error]) => {
             if (typeof error === 'object') {
                 setErrorFromObject(error, `${rootPath}${name}.`);
diff --git a/packages/ra-core/src/form/useApplyInputDefaultValues.ts b/packages/ra-core/src/form/useApplyInputDefaultValues.ts
index fdf927d1f93..eca673f5405 100644
--- a/packages/ra-core/src/form/useApplyInputDefaultValues.ts
+++ b/packages/ra-core/src/form/useApplyInputDefaultValues.ts
@@ -8,7 +8,9 @@ import { InputProps } from './useInput';
  * This hook updates the input default value whenever the record changes
  * It applies either the record value if it has one or the defaultValue if it was specified
  */
-export const useApplyInputDefaultValues = (props: Partial<InputProps>) => {
+export const useApplyInputDefaultValues = (
+    props: Partial<InputProps> & { source: string }
+) => {
     const { defaultValue, source } = props;
     const record = useRecordContext(props);
     const { getValues, resetField } = useFormContext();
diff --git a/packages/ra-core/src/form/useAugmentedForm.ts b/packages/ra-core/src/form/useAugmentedForm.ts
index 5bfed0b974a..aa15260e5d7 100644
--- a/packages/ra-core/src/form/useAugmentedForm.ts
+++ b/packages/ra-core/src/form/useAugmentedForm.ts
@@ -98,7 +98,7 @@ export const useAugmentedForm = (props: UseAugmentedFormProps) => {
 
     // warn when unsaved change
     useWarnWhenUnsavedChanges(
-        warnWhenUnsavedChanges,
+        Boolean(warnWhenUnsavedChanges),
         formRootPathname,
         form.control
     );
diff --git a/packages/ra-core/src/form/useFormGroup.ts b/packages/ra-core/src/form/useFormGroup.ts
index da85384e81f..3eaae18656d 100644
--- a/packages/ra-core/src/form/useFormGroup.ts
+++ b/packages/ra-core/src/form/useFormGroup.ts
@@ -13,7 +13,7 @@ type FieldState = {
 };
 
 type FormGroupState = {
-    errors: object;
+    errors?: object;
     isDirty: boolean;
     isTouched: boolean;
     isValid: boolean;
@@ -128,7 +128,7 @@ export const useFormGroup = (name: string): FormGroupState => {
 export const getFormGroupState = (
     fieldStates: FieldState[]
 ): FormGroupState => {
-    return fieldStates.reduce(
+    return fieldStates.reduce<FormGroupState>(
         (acc, fieldState) => {
             let errors = acc.errors || {};
 
diff --git a/packages/ra-core/src/form/useSuggestions.ts b/packages/ra-core/src/form/useSuggestions.ts
index f42234e4255..3ad791c8d61 100644
--- a/packages/ra-core/src/form/useSuggestions.ts
+++ b/packages/ra-core/src/form/useSuggestions.ts
@@ -174,7 +174,7 @@ export const getSuggestionsFactory = ({
     getChoiceText: (choice: any) => string | ReactElement;
     getChoiceValue: (choice: any) => string;
 }) => filter => {
-    let suggestions = [];
+    let suggestions: any[] = [];
     // if an item is selected and matches the filter
     if (
         selectedItem &&