Bug? java.lang.NullPointerException on Null value

This code causes an error:
But if i write the code in this way errors don't happen::

I don't think is a normal behavior

I guess the logic is that NULL is non existing.

You can't compare something that doesn't exist with a string.

But you can compare a string with being nothing.

This is the expected behavior. As part of the comparison a method is called on the left side object (for non-primitive types). This fails when the left side value is Null.
There is a special case with explicit Nulls on the right side which changes the way the comparison is made (reference check).