From 8678d40115547486481a30bb6cd788af5ae7d8e6 Mon Sep 17 00:00:00 2001
From: subotac <73706465+subotac@users.noreply.github.com>
Date: Wed, 29 Jul 2026 11:10:23 +0300
Subject: [PATCH] fix(arrow-json): validate map value nullability

---
 arrow-json/src/reader/map_array.rs | 15 ++++++---------
 arrow-json/src/reader/mod.rs       | 25 +++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/arrow-json/src/reader/map_array.rs b/arrow-json/src/reader/map_array.rs
index 396b60b1624e..abb035193c39 100644
--- a/arrow-json/src/reader/map_array.rs
+++ b/arrow-json/src/reader/map_array.rs
@@ -130,15 +130,12 @@ impl ArrayDecoder for MapArrayDecoder {
         let key_array = self.keys.decode(tape, &key_pos)?;
         let value_array = self.values.decode(tape, &value_pos)?;
 
-        // SAFETY: fields/arrays match the schema, lengths are equal, no nulls
-        let entries = unsafe {
-            StructArray::new_unchecked_with_length(
-                self.key_value_fields.clone(),
-                vec![key_array, value_array],
-                None,
-                key_pos.len(),
-            )
-        };
+        let entries = StructArray::try_new_with_length(
+            self.key_value_fields.clone(),
+            vec![key_array, value_array],
+            None,
+            key_pos.len(),
+        )?;
 
         let nulls = nulls.as_mut().and_then(|x| x.finish());
         // SAFETY: offsets are built monotonically starting from 0
diff --git a/arrow-json/src/reader/mod.rs b/arrow-json/src/reader/mod.rs
index ea4cbe2664f6..bc95f9562b6f 100644
--- a/arrow-json/src/reader/mod.rs
+++ b/arrow-json/src/reader/mod.rs
@@ -1325,6 +1325,31 @@ mod tests {
         assert_eq!(formatter.value(2).to_string(), "{c: null, a: [baz]}");
     }
 
+    #[test]
+    fn test_map_non_nullable_value() {
+        let map = Field::new_map(
+            "map",
+            Field::MAP_ENTRIES_FIELD_DEFAULT_NAME,
+            Field::new(Field::MAP_KEY_FIELD_DEFAULT_NAME, DataType::Utf8, false),
+            Field::new(Field::MAP_VALUE_FIELD_DEFAULT_NAME, DataType::Utf8, false),
+            false,
+            false,
+        );
+        let schema = Arc::new(Schema::new(vec![map]));
+        let buf = r#"{"map": {"key": null}}"#;
+
+        let err = ReaderBuilder::new(schema)
+            .build(Cursor::new(buf.as_bytes()))
+            .unwrap()
+            .read()
+            .unwrap_err();
+
+        assert_eq!(
+            err.to_string(),
+            "Invalid argument error: Found unmasked nulls for non-nullable StructArray field \"value\""
+        );
+    }
+
     #[test]
     fn test_not_coercing_primitive_into_string_without_flag() {
         let schema = Arc::new(Schema::new(vec![Field::new("a", DataType::Utf8, true)]));