Don't assert nullability in with_keys_field

arrow-array/src/builder/map_builder.rs

@@ -117,21 +117,14 @@ impl<K: ArrayBuilder, V: ArrayBuilder> MapBuilder<K, V> {
     ///
     /// By default, a nullable field is created with the name `keys`
     ///
-    /// Returns an error if the given field is nullable.
-    ///
     /// Note: [`Self::finish`] and [`Self::finish_cloned`] will panic if the
-    /// field's data type does not match that of `K`
-    pub fn with_keys_field(self, field: impl Into<FieldRef>) -> Result<Self, ArrowError> {
-        let field: FieldRef = field.into();
-        if field.is_nullable() {
-            return Err(ArrowError::InvalidArgumentError(format!(
-                "Key field must not be nullable: {field:?}"
-            )));
-        }
-        Ok(Self {
-            key_field: Some(field),
+    /// field's data type does not match that of `K`, or if the keys array
+    /// contains any null values.
+    pub fn with_keys_field(self, field: impl Into<FieldRef>) -> Self {
+        Self {
+            key_field: Some(field.into()),
             ..self
-        })
+        }
     }
 
     /// Override the field passed to [`MapBuilder::new`]
@@ -412,8 +405,7 @@ mod tests {
             Field::new("keys", DataType::Int32, false).with_metadata(key_metadata.clone()),
         );
         let mut builder = MapBuilder::new(None, Int32Builder::new(), Int32Builder::new())
-            .with_keys_field(key_field.clone())
-            .unwrap();
+            .with_keys_field(key_field.clone());
         builder.keys().append_value(1);
         builder.values().append_value(2);
         builder.append(true).unwrap();
@@ -441,12 +433,4 @@ mod tests {
             )
         );
     }
-
-    #[test]
-    fn test_with_nullable_keys_field() {
-        let result = MapBuilder::new(None, Int32Builder::new(), Int32Builder::new())
-            .with_keys_field(Arc::new(Field::new("keys", DataType::Int32, true)));
-
-        assert!(result.is_err());
-    }
 }

arrow-array/src/builder/struct_builder.rs

@@ -297,7 +297,6 @@ pub fn make_builder(datatype: &DataType, capacity: usize) -> Box<dyn ArrayBuilde
                         capacity,
                     )
                     .with_keys_field(fields[0].clone())
-                    .expect("Illegal key field")
                     .with_values_field(fields[1].clone()),
                 )
             }