ValueError: Input contains NaN, infinity or a value too large for dtype('float32')

From this following code :

#importing panda and numpy library and using Skicit-Learn

import numpy as np

import pandas as pd

from sklearn.tree import DecisionTreeClassifier

from sklearn import metrics

With the dataset that i already obtained and after that, i try to :

#creating a Decision tree and fitting it using dataset of train

classifier = DecisionTreeClassifier()

classifier.fit(X_train, y_train)

#creating a Decision tree and fitting it using dataset of train

classifier = DecisionTreeClassifier()

classifier.fit(X_train, y_train)

2. and get this following error too :

This DecisionTreeClassifier instance is not fitted yet. Call 'fit' with appropriate arguments before using this estimator.

with this following code :

#predicting the target column of the test dataset

y_pred = classifier.predict(X_test)

Both error are in the same phyton notebook .

Subject : Phyton