Как проверить поле на пустоту?

<form action="index.php" method="POST" enctype="multipart/form-data">
		<p>имя</p><input type="text" name="name_form"><br>
		<p>возраст</p><input type="text" name="age_form"><br>
		<input type="submit" name="submit">
	</form>

$name_form = $_POST['name_form'];
$age_form = $_POST['age_form'];
$name = "SELECT * FROM users WHERE name = $name_form AND age = $age_form";
$result2 = mysqli_query($conn, $name);

$a = array();

if(mysqli_num_rows($result2) > 0 ) {
	
	while($row = mysqli_fetch_assoc($result2)) {
		$a[] = $row;
	}
} else {
	echo "0 results";
}

print_r($a);