Fix segfault in expand_alternative_phrase_option

string_tree_get_alternative can return NULL

src/expand.c

@@ -1491,8 +1491,12 @@ void expand_alternative_phrase_option(cstring_array *strings, khash_t(str_set) *
             for (; !string_tree_iterator_done(iter); string_tree_iterator_next(iter)) {
                 char_array_clear(temp_string);
                 string_tree_iterator_foreach_token(iter, token, {
+                    if (token == NULL) {
+                        log_debug("token=NULL\n");
+                    } else {
                         log_debug("token=%s\n", token);
                         char_array_append(temp_string, token);
+                    }
                 })
                 char_array_terminate(temp_string);
 

test/test_expand.c

@@ -135,6 +135,15 @@ TEST test_expansions(void) {
     CHECK_CALL(test_expansion_contains_with_languages("Marktstrasse", "markt strasse", options, 1, "de"));
     CHECK_CALL(test_expansion_contains_with_languages("Hoofdstraat", "hoofdstraat", options, 1, "nl"));
     CHECK_CALL(test_expansion_contains_with_languages("มงแตร", "มงแตร", options, 1, "th"));
+
+    PASS();
+}
+
+TEST test_expansion_for_invalid_input(void) {
+    size_t num_expansions;
+
+    // This is tested as the input caused a segfault in expand_alternative_phrase_option
+    libpostal_expand_address("bob-ad1233@blah.co", libpostal_get_default_options(), &num_expansions);
     PASS();
 }
 
@@ -314,6 +323,7 @@ SUITE(libpostal_expansion_tests) {
     RUN_TEST(test_po_box_root_expansions);
     RUN_TEST(test_expansions_language_classifier);
     RUN_TEST(test_expansions_no_options);
+    RUN_TEST(test_expansion_for_invalid_input);
 
     libpostal_teardown();
     libpostal_teardown_language_classifier();