changed selection label to unit in graphics

influxdb.py

@@ -452,7 +452,7 @@ class InfluxDataGetter:
             variable ({"name":(str), "label":(str), "unit":(str)[,"has_potential_target":(bool)]}) : a dictionnary containing the Influx name of the corresponding variable out of the setup_info dict,
             the label to display in the Web GUI, its unit and possibly a boolean value indicating if the variable has a target available. 
         """
-        key = variable["cat"]+variable["unit"]
+        key = variable["cat"]+"_"+variable["unit"] if variable["cat"] != "" else variable["unit"]
         if key not in groups.keys():
             groups[key] = {"tag":key, "unit":variable["unit"], "curves":[]} #tag is set to cat+unit while client is not modified
         groups[key]["curves"].append({