I am trying to make my own server but whenever i try to login it says: failed to login:null. If anyone knows how to fix it please leave a comment. Also is the server.properties file has something to do with it here they are:

#Minecraft server properties
#Mon Jun 17 16:31:30 CDT 2013
generator-settings=
password=true
allow-nether=true
level-name=Pi_Craft
enable-query=false
allow-flight=false
server-port=25565
level-type=DEFAULT
enable-rcon=false
force-gamemode=false
level-seed=
server-ip=192.168.1.7
max-build-height=256
spawn-npcs=true
white-list=false
spawn-animals=true
texture-pack=
snooper-enabled=true
hardcore=false
online-mode=true
pvp=false
difficulty=1
enable-command-block=true
gamemode=0
max-players=20
spawn-monsters=true
generate-structures=true
view-distance=10
spawn-protection=16
motd=Welcome to my new server