Genesis 1:1 says "In the beginning he created heaven and earth" correct? This is talking present tense not past tense as in if it would have read " In the beginning there was heaven and earth" according to Genesis 1 not earth or a heaven existed prior to a god creating them. This makes it an ex-nihilo event.
Do you believe that matter is eternal? This idea is put forth by the Mormons. While you maybe correct in saying that nothing in the Bible indicates a belief in ex-nihilo the very wording in Genesis 1 indicates it is.