Follow-up fixes

Author: DonggeLiu

experiment/measurer/measure_manager.py

@@ -404,7 +404,7 @@ def generate_summary(self, cycle: int, summary_only=False):
                                                       self.profdata_file,
                                                       self.cov_summary_file,
                                                       summary_only=summary_only)
-        if result.retcode != 0:
+        if result is None or result.retcode != 0:
             if cycle != 0:
                 self.logger.error(
                     'Coverage summary json file generation failed for '