There is no "la" in the second sentence because it has a negative form. It will always be the same:
"J'ai du café / Je n'ai pas de café"
please notice that "du" is the contraction of "de le", and therefore, "de le" cannot be used in French, except when the following noun begins with a vowel, so "du" becomes " de l'" because in French we must avoid as much as possible that a syllable ending with a vowel be followed by another vowel, so we can't say "du argent" then we go back to "de le", but erase the "e" to avoid that double wowel, like in this example :
"J'ai de l'argent / Je n'ai pas d'argent"
"J'ai de la chance / je n'ai pas de chance "