difference between timestamps and nullableTimestamps in Laravel 5.4 migration

According to Laravel documentation:

• $table->timestamps(); Adds nullable created_at and updated_at columns.
• $table->nullableTimestamps(); Nullable versions of the timestamps() columns.

I don't understand. In other words, what I read is:

• A creates nullable columns
• B is like A but it creates nullable columns

What did I miss?

via Chebli Mohamed