插入火车（）mlp缺失值

Question

我试图在数据集上训练多层感知器进行非线性回归，但它一直给我这个错误：

Warning message:
In nominalTrainWorkflow(x = x, y = y, wts = weights, info = trainInfo,  :
  There were missing values in resampled performance measures.

我尝试使用R数据集再次执行此操作以查看我的数据是否是问题，但我一直收到错误，我不明白为什么。

我已经尝试添加或删除tuneGrid，trControl，甚至linOut。 由于某些原因，它总是会给我不断的结果。

    library(datasets)
    library(MASS)
    library(caret)
    DP = caret::createDataPartition(Boston$medv, p=0.75, list = F)

    train = Boston[DP,]
    test = Boston[-DP,]
    colnames(train) = colnames(Boston)
    colnames(test) = colnames(Boston)

    mlp = caret::train(medv ~., data = Boston, method = "mlp", trControl = trainControl(method = "cv", number = 3),
                       tuneGrid = expand.grid(size = 1:3), linOut = T, metric = "RMSE")

    Yp = caret::predict.train(mlp, test[,1:13])