Static Class Strings not truly null?

I have a Class for my game that controls the player's hand. It has a boolean called handFull, and when it is true the button that causes the player to grab an object doesn't work. The hand is full, see?

I also have a seperate Class that handles persisting data between scene transitions. It handles player inventory and triggers for the game at large. It is called Persistence. I built it with a public static variable of itself, so that it can be accessed by other Classes in the game (If you've watched the Unity tutorial on Data Persistance, I basically have that, with more variables being remembered) . The player has one inventory slot, and it is handled by a string.

I want the handFull state to persist between scene changes. After all, if you have a Sword in your inventory and your hand is full (handFull == true), it wouldn't do if you shifted scenes, the sword remained in your inventory, but handFull (handled by a non-persistant Class) is suddenly false.

So I wrote some code. It looked like this:

 void Awake (){  
 If (Persistance.mem.Inventory == null){  
 handFull = false  
 }else{  
 handFull = true;  
 }

But every time I ran the script for testing, the game loaded, and handFull was set to true. I went to the Persistance Class, and defined the string Inventory as null, but it did not work. Eventually, I ended up creating a long list of 'Or' statements (if he's not holding a sword or a shield or a bottle or a... then the hand is empty). It works, for this game, but I'd like to have a bit more elegance in my future projects.

What the hell did I do wrong?