Figure out the user's home directory if $HOME is not set

src/libexpr/parser.y

@@ -376,7 +376,7 @@ expr_simple
       $$ = stripIndentation(CUR_POS, data->symbols, *$2);
   }
   | PATH { $$ = new ExprPath(absPath($1, data->basePath)); }
-  | HPATH { $$ = new ExprPath(getEnv("HOME", "") + string{$1 + 1}); }
+  | HPATH { $$ = new ExprPath(getHome() + string{$1 + 1}); }
   | SPATH {
       string path($1 + 1, strlen($1) - 2);
       $$ = new ExprApp(CUR_POS,