Remove Dynamic::NULL, use .as_deref_mut() for this_ptr.

src/func/script.rs

@@ -28,7 +28,7 @@ impl Engine {
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
         scope: &mut Scope,
-        this_ptr: &mut Dynamic,
+        mut this_ptr: Option<&mut Dynamic>,
         _environ: Option<&EncapsulatedEnviron>,
         fn_def: &ScriptFnDef,
         args: &mut FnCallArgs,
@@ -108,12 +108,19 @@ impl Engine {
         #[cfg(feature = "debugging")]
         if self.is_debugger_registered() {
             let node = crate::ast::Stmt::Noop(fn_def.body.position());
-            self.run_debugger(global, caches, scope, this_ptr, &node)?;
+            self.run_debugger(global, caches, scope, this_ptr.as_deref_mut(), &node)?;
         }
 
         // Evaluate the function
         let mut _result: RhaiResult = self
-            .eval_stmt_block(global, caches, scope, this_ptr, &fn_def.body, rewind_scope)
+            .eval_stmt_block(
+                global,
+                caches,
+                scope,
+                this_ptr.as_deref_mut(),
+                &fn_def.body,
+                rewind_scope,
+            )
             .or_else(|err| match *err {
                 // Convert return statement to return value
                 ERR::Return(x, ..) => Ok(x),