when we do:

s = scan.next()

s.length() is definitely greater than 1 as per constraints

but after:

s = s.trim()

all leading and trailing whitespaces are removed

hence if s = " " i.e. only white spaces then

s.trim() will make s.length() == 0

as all white spaces are removed.

In 9th test case if you observe there is

non empty string filled with white spaces

as input hence I had to put that

if condition.