You need to have your eth.defaultAccount set up , right now it might have been not set,due to the fact that get1() is a transnational method and it needs who is invoking it. The automatic public method accessor does not do that,thus you could able to invoke it without problem.
You can do something like at the console.
eth.defaultAccount="0xyoucaccount" // if you know your account address
This will solve the invalid address problem , but you would get another problem when execute the get1() method ,it would return you a transaction hash.
You have two options in cases like this, use event logging, or use a constant function.
Pick your scenario.
This Article could help.