R: adaboost (JOUSBoost package) giving 'Not compatible with requested type'

Question

I have the classic titanic data. Here is the description of the cleaned data.

> str(titanic)
'data.frame':   887 obs. of  7 variables:
 $ Survived               : Factor w/ 2 levels "No","Yes": 1 2 2 2 1 1 1 1 2 2 ...
 $ Pclass                 : int  3 1 3 1 3 3 1 3 3 2 ...
 $ Sex                    : Factor w/ 2 levels "female","male": 2 1 1 1 2 2 2 2 1 1 ...
 $ Age                    : num  22 38 26 35 35 27 54 2 27 14 ...
 $ Siblings.Spouses.Aboard: int  1 1 0 1 0 0 0 3 0 1 ...
 $ Parents.Children.Aboard: int  0 0 0 0 0 0 0 1 2 0 ...
 $ Fare                   : num  7.25 71.28 7.92 53.1 8.05 ...

I first split the data.

smp_size <- floor(0.8 * nrow(titanic))
set.seed(123)
train_ind <- sample(seq_len(nrow(titanic)), size = smp_size)
train <- titanic[train_ind, ]
test <- titanic[-train_ind, ]

Then I changed Survived column to -1 and 1.

train$Survived_ab <- ifelse(train$Survived == 'No', -1, 1)
test$Survived_ab <- ifelse(test$Survived == 'No', -1, 1)

Finally, I ran adaboost algorithm using JOUSBoost package.

dt_ab <- adaboost(X = data.matrix(train[,2:7]), y = train$Survived_ab)

Here are the results.

> print(dt_ab)
NULL
NULL
Dependent Variable: 
No of trees:100
The weights of the trees are:

Tried to predict using the model.

predict_ab <- predict(dt_ab, data.matrix(test[,2:7]), type = 'response')

And got the error below.

Error in predict_adaboost_(tree_list, coeff_vector, newdata, num_examples, : Not compatible with requested type: [type=NULL; target=double].

Why is this?