What you were expecting:
ex. <BooleanInput label="OnOrOff" source="example" defaultValue={false} />
Setting defaultValue on BooleanInput component to false will yield {value: false} in validate function. Fields with defaultValue should be set before validate function runs.

What happened instead:
In: <BooleanInput label="OnOrOff" source="example" defaultValue={false} />
yields: {} in validate function.
Removing defaultValue prop yields same result. Setting defaultValue={true} yields expected result {example: true}
Toggling the BooleanInput field on and then off yields expected result {value: false}
Steps to reproduce:
Create a simple form. Console.log values in validateForm

const validateForm => values => {
console.log('values', values) // <- will yield empty object for boolean fields that have not been toggled
}

<Create {...props}>
     <SimpleForm submitOnEnter={false} validate={validateForm}>
       <BooleanInput label="Deletion" source="example" defaultValue={false} />
     </SimpleForm>
   </Create>

See: https://codesandbox.io/s/9856oq8l0p
Click + and view consoled values.

Environment

• Admin-on-rest version: 1.4.0
• React version: ^15
• Browser: Chrome