Fixed RuntimeError when iterating git config entries with valueless keys.

Author: vruyr

pygit2/config.py

@@ -365,8 +365,8 @@ def raw_name(self) -> bytes:
         return ffi.string(self._entry.name)
 
     @cached_property
-    def raw_value(self) -> bytes:
-        return ffi.string(self.c_value)
+    def raw_value(self) -> bytes | None:
+        return ffi.string(self.c_value) if self.c_value != ffi.NULL else None
 
     @cached_property
     def level(self) -> int:
@@ -379,6 +379,6 @@ def name(self) -> str:
         return self.raw_name.decode('utf-8')
 
     @property
-    def value(self) -> str:
+    def value(self) -> str | None:
         """The entry's value as a string."""
-        return self.raw_value.decode('utf-8')
+        return self.raw_value.decode('utf-8') if self.raw_value is not None else None