在Golearn中使用.Predict（）函数时获取<nil>

I'm playing around with the knnclassifier_iris.go example in the golearn examples folder. I replaced the iris dataset with one of my own, and as long as I train my data on some percentage of the data I read in, all functions work fine and I get some output. However, when I clearly mention a training and testing dataset, and then run predict on the test dataset after fitting the training dataset, I get a nil result when I try to print the predictions. I don't know why I'm getting a nil value, so I would really appreciate some help.

My code:

package main

import (
    "fmt"
    "github.com/sjwhitworth/golearn/base"
    "github.com/sjwhitworth/golearn/evaluation"
    "github.com/sjwhitworth/golearn/knn"
)

func main() {
    trainData, err := base.ParseCSVToInstances("~/Desktop/churn_train.csv", true)
    if err != nil {
        panic(err)
    }
    fmt.Println(trainData)
    testData, err := base.ParseCSVToInstances("~/Desktop/churn_test.csv", false)
    if err != nil {
        panic(err)
    }
    fmt.Println(trainData)
    fmt.Println(testData)

    //Initialises a new KNN classifier
    cls := knn.NewKnnClassifier("euclidean", 2)
    cls.Fit(trainData)

//Calculates the Euclidean distance and returns the most popular label
    predictions := cls.Predict(testData)
    fmt.Println(predictions) //GETTING <NIL> AS OUTPUT

    // Prints precision/recall metrics
    confusionMat, err := evaluation.GetConfusionMatrix(testData, predictions)
    if err != nil {
        panic(fmt.Sprintf("Unable to get confusion matrix: %s", err.Error())) //ERROR CAUSED HERE DUE TO GETTING <NIL>
    }
    fmt.Println(evaluation.GetSummary(confusionMat))

}

(Just in case anybody's stumbled across this on Google). The issue tends to arise when the second ParseCSVToInstances produces instances which are subtly different from the first. To ensure that this isn't the problem, use ParseCSVToTemplatedInstances, so

testData, err := base.ParseCSVToInstances("~/Desktop/churn_test.csv", false)

becomes

 testData, err := base.ParseCSVToTemplatedInstances("~/Desktop/churn_test.csv", false, trainData)