From 834f8c5b38c46c94221c04e930440cdc398d858c Mon Sep 17 00:00:00 2001
From: osipovartem <artemosipov.dev@gmail.com>
Date: Mon, 14 Sep 2026 00:25:27 +0300
Subject: [PATCH] fix(expr): ignore untyped null metadata in values

---
 datafusion/expr/src/logical_plan/builder.rs | 34 ++++++++++++++++-----
 1 file changed, 27 insertions(+), 7 deletions(-)

diff --git a/datafusion/expr/src/logical_plan/builder.rs b/datafusion/expr/src/logical_plan/builder.rs
index 666e60d3a3177..1a1cafc049be1 100644
--- a/datafusion/expr/src/logical_plan/builder.rs
+++ b/datafusion/expr/src/logical_plan/builder.rs
@@ -308,6 +308,14 @@ impl LogicalPlanBuilder {
             let mut nullable = false;
             for (i, row) in values.iter().enumerate() {
                 let value = &row[j];
+                if !nullable && value.nullable(&schema)? {
+                    nullable = true;
+                }
+                let data_type = value.get_type(&schema)?;
+                if data_type == DataType::Null {
+                    continue;
+                }
+
                 let metadata = value.metadata(&schema)?;
                 if let Some(ref cm) = common_metadata {
                     if &metadata != cm {
@@ -320,13 +328,6 @@ impl LogicalPlanBuilder {
                 } else {
                     common_metadata = Some(metadata.clone());
                 }
-                if !nullable && value.nullable(&schema)? {
-                    nullable = true;
-                }
-                let data_type = value.get_type(&schema)?;
-                if data_type == DataType::Null {
-                    continue;
-                }
 
                 if let Some(prev_type) = common_type {
                     // Widen the running type so that it can hold both the
@@ -3252,6 +3253,25 @@ mod tests {
             .is_err()
         );
 
+        // Untyped NULL values adopt the type and metadata inferred from
+        // concrete values, regardless of their position in the column.
+        for values in [
+            vec![
+                vec![lit(ScalarValue::Null)],
+                vec![lit_with_metadata(1, Some(metadata.clone()))],
+            ],
+            vec![
+                vec![lit_with_metadata(1, Some(metadata.clone()))],
+                vec![lit(ScalarValue::Null)],
+            ],
+        ] {
+            let plan = LogicalPlanBuilder::values(values)?.build()?;
+            let field = plan.schema().field(0);
+            assert_eq!(field.data_type(), &DataType::Int32);
+            assert!(field.is_nullable());
+            assert_eq!(*field.metadata(), metadata.to_hashmap());
+        }
+
         Ok(())
     }