Provide default when no branch user param provided

Bug: 147228718
Test: Manual
Change-Id: Ida4a1771c956237bc1149b091d89627582ebaa27
diff --git a/acts/framework/acts/test_utils/power/PowerBaseTest.py b/acts/framework/acts/test_utils/power/PowerBaseTest.py
index 53fbc7a..300c027 100644
--- a/acts/framework/acts/test_utils/power/PowerBaseTest.py
+++ b/acts/framework/acts/test_utils/power/PowerBaseTest.py
@@ -189,9 +189,9 @@
         self.power_logger.set_avg_power(self.power_result.metric_value)
         self.power_logger.set_testbed(self.testbed_name)
 
-        build_id = self.dut.build_info.get('incremental_build_id')
-        branch = self.user_params.get('branch')
-        target = self.dut.device_info.get('flavor')
+        build_id = self.dut.build_info.get('incremental_build_id', '')
+        branch = self.user_params.get('branch', '')
+        target = self.dut.device_info.get('flavor', '')
 
         self.power_logger.set_branch(branch)
         self.power_logger.set_build_id(build_id)