diff --git a/packages/client/src/api.ts b/packages/client/src/api.ts
index 4c77110..e7b6dd7 100644
--- a/packages/client/src/api.ts
+++ b/packages/client/src/api.ts
@@ -324,7 +324,7 @@ async function executeServerAbility(
  */
 export async function executeAbility(
 	name: string,
-	input: AbilityInput = null
+	input?: AbilityInput
 ): Promise< AbilityOutput > {
 	const ability = await getAbility( name );
 	if ( ! ability ) {
diff --git a/packages/client/src/validation.ts b/packages/client/src/validation.ts
index 030da40..8a35002 100644
--- a/packages/client/src/validation.ts
+++ b/packages/client/src/validation.ts
@@ -168,8 +168,9 @@ export function validateValueFromSchema(
 	}
 
 	try {
-		const validate = ajv.compile( args );
-		const valid = validate( value );
+		const { default: defaultValue, ...schemaWithoutDefault } = args;
+		const validate = ajv.compile( schemaWithoutDefault );
+		const valid = validate( value === undefined ? defaultValue : value );
 
 		if ( valid ) {
 			return true;