How to get type from a string in property drawer ?

I’m trying to make a property drawer which will draw a popup field of derived types of the base type the drawer is on. For that to happen, I first need to find the base type of the field the drawer is set on.

But I can’t figure how to get the base type. I always end up with a null value.
I must precise that the type I’m trying to get is a custom serializable class, derived from c# native object, not unity object.

public class SubclassEnumDrawer : PropertyDrawer
    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
        Type baseType = Assembly.GetExecutingAssembly().GetType(property.type);
        // This return null.
        Type baseType =Type.GetType(property.type);
        // This return null too.

You may find a complete answer to what you’re looking for right here : c# - Type Checking: typeof, GetType, or is? - Stack Overflow