The Great Gatsby, hollowy

Could you please tell me the meaning of "hollowy" in the following excerpts from the chapter Four and Six of The Great Gatsby? Does it mean "faintly", "with a cavernous voice", or "with a false ring"

a) I took him into the pantry where he looked a little reproachfully at the Finn. Together we scrutinized the twelve lemon cakes from the delicatessen shop.

“Will they do?” I asked.

“Of course, of course! They’re fine!” and he added hollowly, “...old sport.”

b) A massive and lethargic woman, who had been urging Daisy to play golf with her at the local club tomorrow, spoke in Miss Baedeker’s defence:

“Oh, she’s all right now. When she’s had five or six cocktails she always starts screaming like that. I tell her she ought to leave it alone.”

“I do leave it alone,” affirmed the accused hollowly.