Notice: Trying to get property of non-object in user_variable_get() (line 167 of user_variable.module)

This is due to the following line:

$result->value ? unserialize($result->value) : FALSE

It should read:

empty($result->value) ? FALSE : unserialize($result->value)

(i.e., it should use empty() to check for a valid value, rather than testing a potentially nonexistent variable as a boolean.)