Please help with insert data

Hello,

I want your help

I have this code

case "addads": // 
		$qry = "INSERT INTO 4sale_categories SET catImage1 = '".mysql_real_escape_string(trim($_GET['catImage1']))."' , catImage2 = '".mysql_real_escape_string(trim($_GET['catImage2']))."' , catImage3 = '".mysql_real_escape_string(trim($_GET['catImage3']))."', catImage4 = '".mysql_real_escape_string(trim($_GET['catImage4']))."', catImage5 = '".mysql_real_escape_string(trim($_GET['catImage5']))."', admin_id = '0', phone = '".mysql_real_escape_string(trim($_GET['phone']))."', email = '".mysql_real_escape_string(trim($_GET['email']))."', subcategory = '".mysql_real_escape_string(trim($_GET['subcategoryid']))."', categoryName = '".mysql_real_escape_string(trim($_GET['categoryid']))."', description = '".mysql_real_escape_string(trim($_GET['description']))."', device_token = '".mysql_real_escape_string(trim($_GET['device_token']))."', created = NOW()";
       	$sql = mysql_query($qry);
		

I want to make condition if catImage1 is null insert default value in catimage1 or keep same data  

Thank you