The expression gave down below:
LTRIM(RTRIM(A.EXP_GRAD_TERM)) is not null
Is similar or equivalent to:
A.EXP_GRAD_TERM is not null
An empty string is completely different from NULL, therefore removing spaces from that string which only has spaces makes no effect on the NULL comparison.
I think you are confused because you must have experienced Oracle where empty strings and NULL are both the same thing.
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