add default for FilePointer

src/lib.rs

@@ -58,6 +58,12 @@ pub struct FilePointer<T> {
     _phantom: PhantomData<T>,
 }
 
+impl<T> Default for FilePointer<T> {
+    fn default() -> Self {
+        Self::null()
+    }
+}
+
 unsafe impl<T> Send for FilePointer<T> {}
 unsafe impl<T> Sync for FilePointer<T> {}