be more careful with err

fixes #2824

Author: Vladimir Kotal

opengrok-tools/src/main/python/opengrok_tools/utils/command.py

@@ -62,6 +62,7 @@ def __init__(self, cmd, args_subst=None, args_append=None, logger=None,
         self.redirect_stderr = redirect_stderr
         self.limits = resource_limits
         self.doprint = doprint
+        self.err = None
 
         self.logger = logger or logging.getLogger(__name__)
 
@@ -387,7 +388,10 @@ def geterroutput(self):
         return self.err
 
     def geterroutputstr(self):
-        return "".join(self.err).strip()
+        if self.err:
+            return "".join(self.err).strip()
+        else:
+            return ""
 
     def getstate(self):
         return self.state