Return NULL from Spark char for a NULL scalar input

Author: ranflarion

datafusion/spark/src/function/string/char.rs

@@ -100,6 +100,9 @@ fn spark_chr(args: &[ColumnarValue]) -> Result<ColumnarValue> {
                 }
             }
         }
+        ColumnarValue::Scalar(ScalarValue::Int64(None)) => {
+            Ok(ColumnarValue::Scalar(ScalarValue::Utf8(None)))
+        }
         _ => exec_err!("The argument must be an Int64 array or scalar."),
     }
 }

datafusion/sqllogictest/test_files/spark/string/char.slt

@@ -25,6 +25,11 @@ SELECT char(321::INT);
 ----
 A
 
+query T
+SELECT char(NULL::INT);
+----
+NULL
+
 query T
 SELECT char(a) FROM (VALUES (-1::INT), (0::INT), (65::INT), (321::INT)) AS t(a);
 ----