query select changes

src/sql/query_intermediates.cpp

@@ -14,10 +14,16 @@ query_result<record> query_select_finish::fetch_all()
   return connection_.fetch(compiler.compile(&data_));
 }
 
-record query_select_finish::fetch_one()
+std::optional<record> query_select_finish::fetch_one()
 {
   query_compiler compiler(connection_.dialect());
-  return *connection_.fetch(compiler.compile(&data_)).begin().get();
+  auto result = connection_.fetch(compiler.compile(&data_));
+  auto first = result.begin();
+  if (first == result.end()) {
+    return std::nullopt;
+  }
+
+  return *first.get();
 }
 
 query_context query_select_finish::build() const