adapt tests to strict null

src/log.ts

src/messageprocessor.ts

src/usersyncroniser.ts

test/mocks/discordclient.ts

test/mocks/discordclientfactory.ts

test/mocks/guild.ts

test/mocks/member.ts

test/mocks/message.ts

test/mocks/user.ts

test/test_channelsyncroniser.ts

test/test_discordbot.ts

test/test_log.ts

test/test_matrixeventprocessor.ts

test/test_messageprocessor.ts

test/test_store.ts

test/test_usersyncroniser.ts

test/test_util.ts

tools/chanfix.ts

tools/ghostfix.ts

tools/userClientTools.ts