compatibility: Treat empty version as unknown, not old.

zerver/tests/test_compatibility.py

@@ -20,7 +20,10 @@ class VersionTest(ZulipTestCase):
         15.1.95  <  16.2.96
         16.2.96  =  16.2.96
         20.0.103 >  16.2.96
-    '''.strip().split('\n')]
+    '''.strip().split('\n')] + [
+        ['', '?', '1'],
+        ['', '?', 'a'],
+    ]
 
     def test_version_lt(self) -> None:
         for ver1, cmp, ver2 in self.data:

zerver/views/compatibility.py

@@ -31,6 +31,8 @@ def version_lt(ver1: str, ver2: str) -> Optional[bool]:
     '''
     num1, rest1 = pop_numerals(ver1)
     num2, rest2 = pop_numerals(ver2)
+    if not num1 or not num2:
+        return None
     common_len = min(len(num1), len(num2))
     common_num1, rest_num1 = num1[:common_len], num1[common_len:]
     common_num2, rest_num2 = num2[:common_len], num2[common_len:]