Fix segfaults when no table found

Author: schedutron

src/optimizer/query_to_operator_transformer.cpp

@@ -26,6 +26,7 @@
 #include "parser/statements.h"
 
 #include "catalog/manager.h"
+#include "common/exception.h"
 
 using std::vector;
 using std::shared_ptr;
@@ -231,6 +232,10 @@ void QueryToOperatorTransformer::Visit(parser::InsertStatement *op) {
       catalog::Catalog::GetInstance()
           ->GetDatabaseObject(op->GetDatabaseName(), txn_)
           ->GetTableObject(op->GetTableName());
+  
+  if (target_table == nullptr)
+      throw CatalogException("Table " + op->GetTableName() + " is not found");
+
   if (op->type == InsertType::SELECT) {
     auto insert_expr = std::make_shared<OperatorExpression>(
         LogicalInsertSelect::make(target_table));