Handle empty testcases for AtCoder (e.g. AGC036 B)

onlinejudge/service/atcoder.py

@@ -638,7 +638,11 @@ def _find_sample_tags(cls, soup: bs4.BeautifulSoup) -> Iterator[Tuple[bs4.Tag, b
         for pre in soup.find_all('pre'):
             log.debug('pre tag: %s', str(pre))
             if not pre.string:
-                continue
+                if len(pre.contents):
+                    # <pre> element is not a sample but the input format
+                    continue
+                # the sample is an empty string, so set pre.string as '' instead of None
+                pre.string = ''
 
             def h3_plus(tag):
                 prv = tag.find_previous_sibling()

tests/command_download_atcoder.py

@@ -131,6 +131,26 @@ def test_call_download_atcoder_abc003_4(self):
             },
         ], type='json')
 
+    def test_call_download_atcoder_agc036_b(self):
+        self.snippet_call_download('https://atcoder.jp/contests/agc036/tasks/agc036_b', [
+            {
+                "input": "3 2\n1 2 3\n",
+                "output": "2 3\n"
+            },
+            {
+                "input": "5 10\n1 2 3 2 3\n",
+                "output": "3\n"
+            },
+            {
+                "input": "6 1000000000000\n1 1 2 2 3 3\n",
+                "output": "\n"
+            },
+            {
+                "input": "11 97\n3 1 4 1 5 9 2 6 5 3 5\n",
+                "output": "9 2 6\n"
+            }
+        ], type='json')
+
     def test_call_download_invalid_url(self):
         self.snippet_call_download_raises(requests.exceptions.HTTPError, 'http://abc001.contest.atcoder.jp/tasks/abc001_100')