I filtered the movies to Missing and I deleted the only one I had and this happened.

Version: Radarr Ver. 0.2.0.654
Logs: No logs related to this issue...

I fixed it by deleted the entry in the local storage set as "Missing".

Yeah this is a known issue, there's an issue already open on here (can't currently find it though :/), so gonna close this as a duplicate.
Ran into this just now. Clearing cookies fixed it.
Same here, clearing cookies fixed it. For a minute there I thought I had accidentally deleted my entire library!
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I fixed it by deleted the entry in the local storage set as "Missing".