Ignore nil values on dialogs for event listing

[vitorespindola]

This will fix #28

I'm not a Go developer and maybe this is not the right approach on this error, but this fixed my issue.

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This change is 

[Ulexus]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @vitorespindola)

a discussion (no related file):
There's nothing wrong with the nil check, but I would like to know the scenario in which this occurs. e.Keys() should not be returning nil items in the set.

I'd like to know what is causing that in order to fix it, too.

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[Ulexus]

Reviewed 1 of 1 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @vitorespindola)

[Ulexus]

Reviewable status: complete! all files reviewed, all discussions resolved

[Ulexus]

Reviewed 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved