FIX: Transaction::GetResultSet() now always returns a good reference

Summary

See title. For #11 (closed).

Focus

Is the unique_ptr handling correct?

Test Environment

Just run the unit tests. They failed before the fix.

Check List for the Author

• All automated tests pass
• Reference related Issues
• Up-to-date CHANGELOG.md
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

For further good practices have a look at our review guidelines.

include/caosdb/transaction.h

@@ -365,6 +365,10 @@ public:
   [[nodiscard]] inline auto GetStatus() const noexcept -> TransactionStatus { return this->status; }
 
   [[nodiscard]] inline auto GetResultSet() const noexcept -> const ResultSet & {
+    if (!this->result_set) {
+      this->result_set = std::make_unique<MultiResultSet>(
+          std::move(std::vector<std::unique_ptr<Entity>>()));
+    }
     return *(this->result_set.get());
   }