Fix array_element of empty array

Author: joroKr21

datafusion/functions-nested/src/extract.rs

@@ -224,6 +224,10 @@ where
     i64: TryInto<O>,
 {
     let values = array.values();
+    if values.data_type().is_null() {
+        return Ok(Arc::new(NullArray::new(array.len())));
+    }
+
     let original_data = values.to_data();
     let capacity = Capacities::Array(original_data.len());
 

datafusion/sqllogictest/test_files/array.slt

@@ -1435,6 +1435,12 @@ NULL 23
 NULL 43
 5 NULL
 
+# array_element of empty array
+query T
+select coalesce(array_element([], 1), array_element(NULL, 1), 'ok');
+----
+ok
+
 
 ## array_max
 # array_max scalar function #1 (with positive index)