diff --git a/modules/09_cpp11/src/constexpr_nullptr.cpp b/modules/09_cpp11/src/constexpr_nullptr.cpp
index 445a404..f2a0c79 100644
--- a/modules/09_cpp11/src/constexpr_nullptr.cpp
+++ b/modules/09_cpp11/src/constexpr_nullptr.cpp
@@ -2,7 +2,7 @@
 
 namespace cpp11 {
 
-auto to_index(Color color) -> int {
+auto to_index(const Color color) -> int {
     switch (color) {
         case Color::Red: return 0;
         case Color::Green: return 1;
@@ -11,14 +11,12 @@ auto to_index(Color color) -> int {
     return -1;
 }
 
-auto square(int value) -> int {
-    (void)value;
-    return 0;
+auto square(const int value) -> int {
+    return value * value;
 }
 
 auto find_null(int* ptr) -> int* {
-    (void)ptr;
-    return nullptr;
+    return ptr;
 }
 
 }  // namespace cpp11