Overwrite to None if n=0

vm/src/vm/vm_core.rs

@@ -1105,7 +1105,7 @@ impl VirtualMachine {
     /// Fetches add_mod & mul_mod builtins according to the optional arguments and executes `fill_memory`
     /// Returns an error if either of this optional parameters is true but the corresponding builtin is not present
     /// Verifies that both builtin's (if present) batch sizes match the batch_size arg if set
-    // This method is needed as running `fill_memory` direclty from outside the vm struct would require cloning the builtin runners to avoid double borrowing
+    // This method is needed as running `fill_memory` directly from outside the vm struct would require cloning the builtin runners to avoid double borrowing
     pub fn mod_builtin_fill_memory(
         &mut self,
         add_mod_ptr_n: Option<(Relocatable, usize)>,
@@ -1119,6 +1119,9 @@ impl VirtualMachine {
             VirtualMachineError,
         > {
             if let Some((ptr, n)) = mod_params {
+                if n == 0 {
+                    return Ok(None);
+                }
                 let mod_builtin = self
                     .builtin_runners
                     .iter()