java.lang.nullPointerException

Console console = System.console(); 
String attendeeLastName = console.readLine("Enter your last name: "); 
lastName = attendeeLastName; 

if ( letter <= 'M' ){ 
...
}

if ( letter >= 'A' && letter <= 'M' ){ 
...
} 

import java.io.Console;

public class ConferenceRegistrationAssistant {
    static Console console = System.console();
    private static String attendeeLastName;
    private static char letter;
    private static int line;

    public static void main(String[] args) {
        getLineFor();
        System.out.println("Person with the last name of: " + attendeeLastName.toLowerCase() + ". Was sent to line: " + line); //In the println statement the user's input will be shown in lowercase and not caps.
    }

    public static int getLineFor() { /* If the last name is between A thru M send them to line 1 Otherwise send them to line 2 */ 
        attendeeLastName = console.readLine("What is your last name?: ");
        attendeeLastName = attendeeLastName.toUpperCase(); //Now the casing doesn't matter for the user input, it will always be in caps, when assigned to 'letter'.
        letter = attendeeLastName.charAt(0);               //Otherwise, if a user typed in any last name that starts with a lowercase 'm', would be sent to line 2.
                                                           //Because in your if condition, you're checking for a last name that starts with an uppercase 'M'.

        if(letter <= 'M') { //All you need to do for your if condition is check for a letter that is less than or equal to M, which will automatically cover (A - M).
            line = 1;       
            return line;
        } else { //Any last names that start with (N - Z) will be automatically assigned to line 2.
            line = 2;
            return line;
        }
    }
}