Skip alarm evaluation if no value is set for attribute

Author: mliszcz

cppapi/server/attribute.cpp

@@ -1681,6 +1681,14 @@ bool Attribute::check_alarm()
 		return returned;
 	}
 
+// Skip alarm evaluation if no value for this attribute was provided during last read.
+
+	if (!get_value_flag())
+	{
+		DEV_WARN_STREAM(dev) << "Attribute has no value, skipping alarm evaluation for: " << get_name() << std::endl;
+		return false;
+	}
+
 //
 // Get the monitor protecting device att config
 //