Fix check if stderr is empty (#613)

Author: davidkopp

runner.py

@@ -961,7 +961,7 @@ def start_metric_providers(self, allow_container=True, allow_other=True):
 
             stderr_read = metric_provider.get_stderr()
             print(f"Stderr check on {metric_provider.__class__.__name__}")
-            if stderr_read is not None and str(stderr_read) is not '':
+            if stderr_read is not None and str(stderr_read):
                 raise RuntimeError(f"Stderr on {metric_provider.__class__.__name__} was NOT empty: {stderr_read}")
 
 
@@ -1095,7 +1095,7 @@ def stop_metric_providers(self):
                 continue
 
             stderr_read = metric_provider.get_stderr()
-            if stderr_read is not None and str(stderr_read) is not '':
+            if stderr_read is not None and str(stderr_read):
                 errors.append(f"Stderr on {metric_provider.__class__.__name__} was NOT empty: {stderr_read}")
 
             metric_provider.stop_profiling()