Make peeking the Value stack return Value.NULL if it's empty

.gitignore

@@ -1,3 +1,5 @@
 .gradle
 .idea
-build
+build
+/src/test/generated_tests/
+/out/

src/main/java/org/meteordev/starscript/Starscript.java

@@ -125,11 +125,13 @@ public Value pop() {
 
     /** Returns a value from the stack without removing it. */
     public Value peek() {
+        if (stack.size() == 0) return Value.null_();
         return stack.peek();
     }
 
     /** Returns a value from the stack with an offset without removing it. */
     public Value peek(int offset) {
+        if (stack.size() <= offset) return Value.null_();
         return stack.peek(offset);
     }
 

src/main/java/org/meteordev/starscript/utils/Stack.java

@@ -34,4 +34,8 @@ public T peek() {
     public T peek(int offset) {
         return items[size - 1 - offset];
     }
+
+    public int size() {
+        return size;
+    }
 }