Fixed failing to accept dictionary full of nulls

src/array/dictionary/mod.rs

@@ -119,7 +119,9 @@ impl<K: DictionaryKey> DictionaryArray<K> {
     ) -> Result<Self, Error> {
         check_data_type(K::KEY_TYPE, &data_type, values.data_type())?;
 
-        check_indexes(keys.values(), values.len())?;
+        if keys.null_count() != keys.len() {
+            check_indexes(keys.values(), values.len())?;
+        }
 
         Ok(Self {
             data_type,

tests/it/array/dictionary/mod.rs

@@ -40,6 +40,20 @@ fn try_new_incorrect_key() {
     assert!(r);
 }
 
+#[test]
+fn try_new_nulls() {
+    let key: Option<u32> = None;
+    let keys = PrimitiveArray::from_iter([key]);
+    let value: &[&str] = &[];
+    let values = Utf8Array::<i32>::from_slice(value);
+
+    let data_type =
+        DataType::Dictionary(u32::KEY_TYPE, Box::new(values.data_type().clone()), false);
+    let r = DictionaryArray::try_new(data_type, keys, values.boxed()).is_ok();
+
+    assert!(r);
+}
+
 #[test]
 fn try_new_incorrect_dt() {
     let values = Utf8Array::<i32>::from_slice(["a", "aa"]);