Error occured when adding user by email+password

[Youtch]

Please could you check the code, to finish to write this beautiful app :
When I add new user by email+password an error occures : remote data node can't be added if it include specials chars : but "." is needed to type email address !

Morevover it could be a good idea to indicate how to create Firebase project, and how to create firebase options file named firebase_options.dart, which must be included in the /lib folder to make possible communication with Firebase Database !