Error at line 253

[Tahseen-Mulla]

Your case study has helped my students to understand well about sentiment analysis
But there is an error at line 253
x_train, x_valid, y_train, y_valid = train_test_split(x, y, test_size = 0.25, random_state = 42)

Can you please tell me why am i getting such error?
I am trying to resolve from last week, but couldnt

The error says:

Please guide me and my students through this

Thanks in advance