template/generic instantiation of `map` warning

[pmags]

I'm working with derived enum types and I'm encountering errors 
"template/generic instantiation of map" warnings that I don't understand.

Here's a shortened version of my code:
    
    
    import sequtils, tables
    
    type
      AmbigNucleotide = enum
        T, A, G, C, U, W, S, M, K, R, Y, B, D, H, V, N
      DNA = range[T..C]
      RNA = range[A..U]
    
    const
      tblDNAtoRNA = {A: A, T: U, G: G, C: C}.toTable
    
    proc transcribe(n: DNA): RNA =
      RNA tblDNAtoRNA[n]
    
    proc transcribe(ns: seq[DNA]): seq[RNA] =
      map(ns, transcribe)
      # I've also tried map[DNA,RNA](ns, transcribe) with the same results
    
    let dna = @[DNA A, T, T, G, C, C, T, T]
    let rna = transcribe(dna)
    
    echo "DNA: ", dna
    echo "Transcribed RNA: ", rna
    
    
    Run

The code above compiles and works but I get the following warnings (edited to 
highlight key lines):
    
    
    example02.nim(17, 6) template/generic instantiation of `map` from here
    sequtils.nim(311, 10) Warning: Cannot prove that 'result' is initialized. 
This will become a compile time error in the future. [ProveInit]
    
    
    Run

My key point of confusion is why this is a generic instantiation of map at all. 
It seems the types are well defined.