fix

Author: robert3005

encodings/runend/src/compute/nan_count.rs

@@ -27,7 +27,7 @@ where
 /// This will update the stats set of this array (as a side effect).
 pub fn nan_count(array: &dyn Array) -> VortexResult<Option<usize>> {
     if array.is_empty() || array.valid_count()? == 0 {
-        return Ok(None);
+        return Ok(Some(0));
     }
 
     let nan_count = array