     // Determine the appropriate Integer key, based on the given fundamentalFrequency.
     let roundedFrequency = Int(round(fundamentalFrequency))
     // Look for existing keys close to the rounded frequency.
-    var frequencies: [Double]? = nil
+    var frequencies: [Double]?
 
     let sortedFundamentalFrequencies = mapOfFundamentalFrequencies.sorted {
       let (roundedFrequency1, _) = $0

  private static func gcd(_ a: Int, _ b: Int) -> Int {
    var a = a
    var b = b
    while (b > 0) {
      let temp = b
      b = a % b
      a = temp

        }
      }
    }
    if foundHarmonicRatio {
      return Harmonic.addHarmonic(peakA: peakA, peakB: peakB, termA: termA, termB: termB)
    }
    return nil
