SwiftOCRTraining doesn't generate any trainData and testData

[songhailiang]

Hi,
I'm trying to training the app using SwiftOCRTraining,

SwiftOCRTraining().trainWithCharSet()

but i find after the generate method finished, the trainData does not have any items

let trainData = generateRealisticCharSet(numberOfTrainImages/4)
// trainData is empty

this is caused by the blobs is not equal to 6,

            if blobs.count == 6 {
                for blobIndex in 0..<blobs.count {
                    let blob = blobs[blobIndex]
                    let imageData = ocrInstance.convertImageToFloatArray(blob.0)
                    var imageAnswer = [Float](repeating: 0, count: recognizableCharacters.characters.count)
                    if let index = Array(recognizableCharacters.characters).index(of: Array(code.characters)[blobIndex]) {
                        imageAnswer[index] = 1
                    }   
                    trainingSet.append((imageData,imageAnswer))
                }
            }

I don't know why this happened, can anybody help me?
Many thanks.