Fix and test NULL keys in LEFT / LEFT ONLY in block map join (#9847)

Author: yumkam

ydb/library/yql/minikql/comp_nodes/mkql_block_map_join.cpp

@@ -257,15 +257,13 @@ using TState = TBlockJoinState<RightRequired>;
                 while (blockState.IsNotFull() && blockState.NextRow()) {
                     const auto key = MakeKeysTuple(blockState);
                     if constexpr (WithoutRight) {
-                        if (key && Dict_.Contains(key) == RightRequired) {
+                        if ((key && Dict_.Contains(key)) == RightRequired) {
                             blockState.CopyRow();
                         }
-                    } else if constexpr (RightRequired) {
-                        if (NUdf::TUnboxedValue lookup; key && (lookup = Dict_.Lookup(key))) {
-                            blockState.MakeRow(lookup);
-                        }
-                    } else {
-                        blockState.MakeRow(Dict_.Lookup(key));
+                    } else if (NUdf::TUnboxedValue lookup; key && (lookup = Dict_.Lookup(key))) {
+                        blockState.MakeRow(lookup);
+                    } else if constexpr (!RightRequired) {
+                        blockState.MakeRow(NUdf::TUnboxedValue());
                     }
                 }
                 if (blockState.IsNotFull() && !blockState.IsFinished()) {