"Warning: Cannot prove that 'result' is initialized"

[rxi]

Unsure what I should be doing differently in the following code as to prevent 
the warnings:
    
    
    import strutils
    
    type MouseButton* = enum
      mbLeft = 1
      mbMiddle = 2
      mbRight = 3
    
    let s = "mbLeft"
    let m = parseEnum[MouseButton](s)
    echo m
    

Warnings:
    
    
    test.nim(9, 18) template/generic instantiation from here
    lib/pure/strutils.nim(994, 3) Warning: Cannot prove that 'result' is 
initialized. This will become a compile time error in the future. [ProveInit]
    test.nim(9, 5) Warning: Cannot prove that 'm' is initialized. This will 
become a compile time error in the future. [ProveInit]
    

Any suggestions would be appreciated, thanks!