fast path all null

crates/polars-ops/src/series/ops/cut.rs

@@ -131,21 +131,19 @@ pub fn qcut(
 ) -> PolarsResult<Series> {
     polars_ensure!(!probs.iter().any(|x| x.is_nan()), ComputeError: "quantiles cannot be NaN");
 
+    if s.null_count() == s.len() {
+        // If we only have nulls we don't have any breakpoints.
+        return Ok(Series::full_null(
+            s.name().clone(),
+            s.len(),
+            &DataType::Categorical(None, Default::default()),
+        ));
+    }
+
     let s = s.cast(&DataType::Float64)?;
     let s2 = s.sort(SortOptions::default())?;
     let ca = s2.f64()?;
 
-    if ca.null_count() == ca.len() {
-        // If we only have nulls we don't have any breakpoints.
-        return cut(
-            &s,
-            vec![],
-            None::<Vec<PlSmallStr>>,
-            left_closed,
-            include_breaks,
-        );
-    }
-
     let f = |&p| {
         ca.quantile(p, QuantileInterpolOptions::Linear)
             .unwrap()