HdMapUtils::getStopLinePolygon doesn't check if given lanelet is a stop line

[gmajrobotec]

Description
Function “getStopLinePolygon” does not check if “lanelet_id” represents a stopline. Any linesting can be passed and it will be transformed to “std::vector” unconditionally.

To Reproduce

1. Add this testcase to the test_hdmap_utils.cpp file.
2. Run the test suite.
3. In the attached example, the function “getPreviousLanelets” will return a non empty vector for lanelet:Id 34574, which is a linestring on the path, not a stop line.

TEST(HdMapUtils, getStopLinePolygon_example)
{
  const auto hdmap_utils = makeHdMapUtilsSharedPointer();

  const lanelet::Id id = 120635;

  const auto stop_lines = hdmap_utils->getStopLineIdsOnPath(
    lanelet::Ids{34408, 34633, 34579, 34780, 34675, 34744, 34690, 34759, 34576, 34570, 34564});

  const lanelet::Ids actual_stop_lines{id};

  const auto polygon = hdmap_utils->getStopLinePolygon(id);
  const auto polygon_fake = hdmap_utils->getStopLinePolygon(34574);

  EXPECT_EQ(stop_lines, actual_stop_lines);
  EXPECT_TRUE(polygon.size());
  EXPECT_FALSE(polygon_fake.size());
}

Solution
There should be added a check whether the passed lanelet ID is actually a stop line, or a note should be left stating that the “lanelet_id” is assumed to be a stop line, or the function should be renamed to something like “getLineStringPolygon”.