SSJ2 said:
Emotionless =\= negative, though she was pretty negative for a short amount of time after joining the crew I guess.
She also had some pretty negative speechs, like when she said that maybe Nami and co. were brutally murdered by the ghosts when Nami was riding the mini merry and they just disappeared.
Once Perona saw how Usopp withstood her ghosts, she said that people, as long as they are living, look forward to something, which implies not doing so might be the key to withstanding her power:
And Usopp, even though pretty negative himself, still aspires to become a brave warrior of the sea. Even though Robin also really wishes to know what happened in the missed century, by the way Perona described the trait of someone whose her power would better pick up on, it seems better linked to an emotionless, not-driven by anything person.