Remove error promotion from COALESCE

Author: frankmcsherry

src/expr/src/scalar.rs

@@ -1237,11 +1237,7 @@ impl MirScalarExpr {
                             let mut prior_exprs = BTreeSet::new();
                             exprs.retain(|e| prior_exprs.insert(e.clone()));
 
-                            if let Some(expr) = exprs.iter_mut().find(|e| e.is_literal_err()) {
-                                // One of the remaining arguments is an error, so
-                                // just replace the entire coalesce with that error.
-                                *e = expr.take();
-                            } else if exprs.len() == 1 {
+                            if exprs.len() == 1 {
                                 // Only one argument, so the coalesce is a no-op.
                                 *e = exprs[0].take();
                             }