Don't raise RuntimeError if git_submodule_url returns NULL

Author: jorio

pygit2/submodules.py

@@ -31,7 +31,7 @@
 from .enums import SubmoduleIgnore, SubmoduleStatus
 from .errors import check_error
 from .ffi import ffi, C
-from .utils import to_bytes
+from .utils import to_bytes, maybe_string
 
 # Need BaseRepository for type hints, but don't let it cause a circular dependency
 if TYPE_CHECKING:
@@ -129,10 +129,10 @@ def path(self):
         return ffi.string(path).decode('utf-8')
 
     @property
-    def url(self):
+    def url(self) -> Union[str, None]:
         """URL of the submodule."""
         url = C.git_submodule_url(self._subm)
-        return ffi.string(url).decode('utf-8')
+        return maybe_string(url)
 
     @property
     def branch(self):

test/test_submodule.py

@@ -106,6 +106,15 @@ def test_url(repo):
     assert SUBM_URL == s.url
 
 
+def test_missing_url(repo):
+    # Remove "url" from .gitmodules
+    with open(Path(repo.workdir, '.gitmodules'), 'wt') as f:
+        f.write('[submodule "TestGitRepository"]\n')
+        f.write('\tpath = TestGitRepository\n')
+    s = repo.submodules[SUBM_PATH]
+    assert not s.url
+
+
 @utils.requires_network
 def test_init_and_update(repo):
     subrepo_file_path = Path(repo.workdir) / SUBM_PATH / 'master.txt'