Expression tag initializing with -1 value

expression I am using is

tag({operators_path}+ "CECOEL" +"/REG_ZON_CCGT/SRS/"+{TagName})

when I am restarting the gateway very first time then my expression tag value is becoming -1 from nowhere, the value of tag({operators_path}+ "CECOEL" +"/REG_ZON_CCGT/SRS/"+{TagName}) can never be -1, its either 0 or 1.

I am suspecting that if the dependent tag ( i.e tag({operators_path}+ "p1" +"/path/to/"+{TagName}) ) is not set to defined value then this behaviour is happening.

Anyone know about this?