Fix empty fs_uniquifier for existing users.

Fixes #109
Thanks for all your help @hgy59 @mreid-tt

migrations/versions/76d559b4e873_add_fs_uniquifier.py

@@ -13,16 +13,18 @@
 
 
 def upgrade():
-    # ### commands auto generated by Alembic - please adjust! ###
     op.add_column(
-        "user", sa.Column("fs_uniquifier", sa.String(length=255), nullable=False)
+        "user",
+        sa.Column(
+            "fs_uniquifier",
+            sa.String(length=255),
+            nullable=False,
+            server_default=sa.text("md5(random()::text)"),
+        ),
     )
-    op.create_unique_constraint(None, "user", ["fs_uniquifier"])
-    # ### end Alembic commands ###
+    op.create_unique_constraint("user_fs_uniquifier_key", "user", ["fs_uniquifier"])
 
 
 def downgrade():
-    # ### commands auto generated by Alembic - please adjust! ###
-    op.drop_constraint(None, "user", type_="unique")
+    op.drop_constraint("user_fs_uniquifier_key", "user", type_="unique")
     op.drop_column("user", "fs_uniquifier")
-    # ### end Alembic commands ###