Actually, argv[i] cannot has a length of 0, so let's compare here against 1, meaning there was just a '-' was passed.

kwh-cost.c

@@ -40,7 +40,7 @@ int parse_arguments(const int argc, const char *const *const argv,
     for (int i = 1, pos = 0; i < argc; ++i)
         if (argv[i][0] == '-') {
             size_t l = strlen(argv[i]);
-            if (l < 2)
+            if (l == 1)
                 return 99;
             if (argv[i][1] == 'h' || (argv[i][1] == '-' && l > 2 && argv[i][2] == 'h'))
                 return 1;