mkDerivation: show meaningful error when version is set to null

instead of `Cannot coerce null to string`

pkgs/stdenv/generic/make-derivation.nix

@@ -300,6 +300,7 @@ else let
           hostSuffix = lib.optionalString
             (stdenv.hostPlatform != stdenv.buildPlatform && !dontAddHostSuffix)
             "-${stdenv.hostPlatform.config}";
+
           # Disambiguate statically built packages. This was originally
           # introduce as a means to prevent nix-env to get confused between
           # nix and nixStatic. This should be also achieved by moving the
@@ -310,7 +311,10 @@ else let
         lib.strings.sanitizeDerivationName (
           if attrs ? name
           then attrs.name + hostSuffix
-          else "${attrs.pname}${staticMarker}${hostSuffix}-${attrs.version}"
+          else
+            # we cannot coerce null to a string below
+            assert lib.assertMsg (attrs ? version && attrs.version != null) "The ‘version’ attribute cannot be null.";
+            "${attrs.pname}${staticMarker}${hostSuffix}-${attrs.version}"
         );
     }) // lib.optionalAttrs __structuredAttrs { env = checkedEnv; } // {
       builder = attrs.realBuilder or stdenv.shell;