Fix type of ExecutionOptions::time_zone (#16569)

Previously the field was optional. However, when set to a None value, it
would trigger invalid behavior, with `timestamp with time zone` type
being parsed as if it was just `timestamp` type.

Author: findepi

datafusion/common/src/config.rs

@@ -364,7 +364,7 @@ config_namespace! {
         ///
         /// Some functions, e.g. `EXTRACT(HOUR from SOME_TIME)`, shift the underlying datetime
         /// according to this time zone, and then extract the hour
-        pub time_zone: Option<String>, default = Some("+00:00".into())
+        pub time_zone: String, default = "+00:00".into()
 
         /// Parquet options
         pub parquet: ParquetOptions, default = Default::default()

datafusion/sql/src/planner.rs

@@ -616,7 +616,7 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
                     // Timestamp With Time Zone
                     // INPUT : [SQLDataType]   TimestampTz + [Config] Time Zone
                     // OUTPUT: [ArrowDataType] Timestamp<TimeUnit, Some(Time Zone)>
-                    self.context_provider.options().execution.time_zone.clone()
+                    Some(self.context_provider.options().execution.time_zone.clone())
                 } else {
                     // Timestamp Without Time zone
                     None