diff --git a/src/ics_sim/Device.py b/src/ics_sim/Device.py
index 6d90fb1..548afc3 100755
--- a/src/ics_sim/Device.py
+++ b/src/ics_sim/Device.py
@@ -40,9 +40,9 @@ def add_sensor(self, tag, fault):
     def read(self, tag):
         if tag in self._sensors.keys():
             value = self._get(tag)
-            # if value is None:
-            #     print(f"The tag: {tag} recieved null value from databse. return -1!")
-            #     return -1
+            if value is None:   # todo: we have to comment this section
+                print(f"The tag: {tag} recieved null value from databse. return -1!")
+                return -1
             value += random.uniform(value, -1 * value) * self._sensors[tag]
             return value
         else:
diff --git a/src/ics_sim/connectors.py b/src/ics_sim/connectors.py
index 37bea36..ce20ec6 100755
--- a/src/ics_sim/connectors.py
+++ b/src/ics_sim/connectors.py
@@ -77,7 +77,7 @@ def set(self, key, value):
                 return value
 
             except sqlite3.Error as e:
-                error('_set in ICSSIM connection %s: ' % e.args[0])
+                error(f'_set in ICSSIM connection {e.args[0]} for setting tag {key}')
 
     def get(self, key):
         get_query = """SELECT {} FROM {} WHERE {} = ?""".format(
@@ -94,7 +94,7 @@ def get(self, key):
                 return record[0]
 
             except sqlite3.Error as e:
-                error('_get in ICSSIM connection %s: ' % e.args[0])
+                error(f'_get in ICSSIM connection {e.args[0]} for getting tag {key}')
 
 
 class MemcacheConnector(Connector):