fix(formiks): initialize FormikCheckbox form value on mount

src/formiks/FormikCheckbox.tsx

@@ -1,5 +1,5 @@
 import { useField } from 'formik'
-import { useMemo } from 'react'
+import { useEffect, useMemo } from 'react'
 
 import { Checkbox } from '../fields/Checkbox'
 
@@ -14,6 +14,17 @@ export function FormikCheckbox({ name, ...originalProps }: FormikCheckboxProps)
   // eslint-disable-next-line react-hooks/exhaustive-deps
   const isDefaultChecked = useMemo(() => Boolean(field.value), [])
 
+  // A checkbox must initialize its Formik value on mount:
+  // it wouldn't make sense to keep it as `undefined` since `undefined` means `false` in the case of a checkbox
+  useEffect(
+    () => {
+      helpers.setValue(isDefaultChecked)
+    },
+
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+    []
+  )
+
   return (
     <Checkbox
       defaultChecked={isDefaultChecked}