diff --git a/mx-rust-semantics/main/glue.md b/mx-rust-semantics/main/glue.md
index 0b07de7..9b9162d 100644
--- a/mx-rust-semantics/main/glue.md
+++ b/mx-rust-semantics/main/glue.md
@@ -17,6 +17,7 @@ module MX-RUST-GLUE
           ...
       </k>
       <values> Values:Map => Values[ValueId <- V] </values>
+      requires ValueId >=Int 0
 
   rule
       (.K => mxRustEmptyValue(T))
diff --git a/mx-rust-semantics/main/modules/storage.md b/mx-rust-semantics/main/modules/storage.md
index 2d40490..582f64b 100644
--- a/mx-rust-semantics/main/modules/storage.md
+++ b/mx-rust-semantics/main/modules/storage.md
@@ -49,6 +49,38 @@ module MX-RUST-MODULES-STORAGE
             ...
         </values>
 
+    rule
+        <k>
+            normalizedMethodCall
+                ( #token("SingleValueMapper", "Identifier"):Identifier #as Type:Identifier
+                , #token("set_if_empty", "Identifier"):Identifier
+                ,   ( ptr(SelfId:Int)
+                    , ptr(ValueId:Int)
+                    , .NormalizedCallParams
+                    )
+                )
+            => MX#storageLoad(mxStringValue(StorageKey), rustDestination(-1, noType))
+                ~> setIfEmpty
+                ~> MX#storageStore(mxStringValue(StorageKey), wrappedRust(V))
+            ...
+        </k>
+        <values>
+            SelfId |-> struct
+                        ( Type
+                        , #token("storage_key", "Identifier"):Identifier |-> StorageKeyId:Int
+                            _:Map
+                        )
+            StorageKeyId |-> StorageKey:String
+            ValueId |-> V:Value
+            ...
+        </values>
+
+    rule mxRustEmptyValue(noType) ~> storeHostValue(...) ~> setIfEmpty
+        => .K
+    rule storeHostValue(... value: wrappedRust(_))
+          ~> setIfEmpty ~> MX#storageStore(_)
+        => .K
+
     rule
         <k>
             normalizedMethodCall
@@ -75,6 +107,7 @@ module MX-RUST-MODULES-STORAGE
         </values>
         <next-value-id> NextId:Int => NextId +Int 1 </next-value-id>
 
+    syntax MxRustInstruction ::= "setIfEmpty"
 endmodule
 
 ```
diff --git a/mx-rust-semantics/main/representation.md b/mx-rust-semantics/main/representation.md
index 39c5be5..a17f947 100644
--- a/mx-rust-semantics/main/representation.md
+++ b/mx-rust-semantics/main/representation.md
@@ -11,7 +11,7 @@ module MX-RUST-REPRESENTATION
                                 | mxValueToRust(Type)
                                 | mxRustLoadPtr(Int)
 
-    syntax MxRustType ::= "BigUint"
+    syntax MxRustType ::= "noType" | "BigUint"
     syntax MxRustTypeOrError ::= MxRustType | SemanticsError
     syntax Value ::= MxRustType