Fix crash of null path expression. (#3915)

* Fix crash of null path expression.

* Add test case.

Co-authored-by: jakevin <30525741+jackwener@users.noreply.github.com>

src/graph/planner/match/MatchClausePlanner.cpp

@@ -409,7 +409,7 @@ Status MatchClausePlanner::projectColumnsBySymbols(MatchClauseContext* matchClau
  auto iter = std::find_if(aliases.begin(), aliases.end(), [](const auto& alias) {
  return alias.second == AliasType::kPath;
  });
- if (iter != aliases.end()) {
+ if (iter != aliases.end() && path.pathBuild != nullptr) {
  auto& alias = iter->first;
  columns->addColumn(buildPathColumn(path.pathBuild, alias));
  colNames.emplace_back(alias);

tests/tck/features/bugfix/CrashWhenNullPathExpr.feature

@@ -0,0 +1,17 @@
+# Copyright (c) 2022 vesoft inc. All rights reserved.
+#
+# This source code is licensed under Apache 2.0 License.
+Feature: Test crash when null path expression
+
+ Background:
+ Given a graph with space named "nba"
+
+ Scenario: Null path expression in multiple patterns
+ When executing query:
+ """
+ MATCH (p:player {name: 'Yao Ming'} ), (t:team {name: 'Rockets'}), pth = (p)-[:serve*1..4]-(t)
+ RETURN pth
+ """
+ Then the result should be, in any order, with relax comparison:
+ | pth |
+ | <("Yao Ming":player{age:38,name:"Yao Ming"})-[:serve@0{end_year:2011,start_year:2002}]->("Rockets":team{name:"Rockets"})> |