      def update_config(self):
          """ Update config with selected values """
          for section, items in self.tk_vars.items():
              for item, value in items.items():
                  new_value = str(value.get())
                  old_value = self.config.config[section][item]
                  if new_value != old_value:
                      logger.trace("Updating config: %s, %s from %s to %s",
                                   section, item, old_value, new_value)
                      self.config.config[section][item] = str(value.get())
 
</s> remove                     self.config.config[section][item] = str(value.get())
 </s> add                     self.config.config[section][item] = new_value
                try:
                    new_value = str(value.get())
                except tk.TclError as err:
                    # When manually filling in text fields, blank values will
                    # raise an error on numeric datatypes so return 0
                    logger.debug("Error getting value. Defaulting to 0. Error: %s", str(err))
                    new_value = str(0)
      def update_config(self):
          """ Update config with selected values """
          for section, items in self.tk_vars.items():
              for item, value in items.items():
                try:
                    new_value = str(value.get())
                except tk.TclError as err:
                    # When manually filling in text fields, blank values will
                    # raise an error on numeric datatypes so return 0
                    logger.debug("Error getting value. Defaulting to 0. Error: %s", str(err))
                    new_value = str(0)
                  old_value = self.config.config[section][item]
                  if new_value != old_value:
                      logger.trace("Updating config: %s, %s from %s to %s",
                                   section, item, old_value, new_value)
                      self.config.config[section][item] = str(value.get())
keep keep keep keep replace keep keep keep keep keep
 Bugfix: Preview Tool - empty tk_var string

- Replace empty tk_vars with 0 for numerical values 
tools/preview.py