What is the meaning of the term bah humbug in A Christmas Carol?

"WALKER"

Oxford English Dictionary XII: 44. "More fully, Hookey Walker." [Always written with initial capital; probably a use of the surname Walker.] An exclamation expressive of incredulity, Also occasionally as a sb. (= 'humbug'), as in "That is all Walker."

1811 Lex. Balatronicum, Hookee Walker, an expression signifying that the story is not true, or that the thing will not occur.

Eric Partridge, A Dictionary of Slang and Unconventional English (London: Routledge and Kegan Paul, 1949) 403.

Hooky Walker! A phrase signifying that something either is not true or will not occur: (low) colloquial, from ca. 1810. Lex. Bal. Also Hook[e]y!, as in Bee, and by hooky!, as in Manchon.‹2. Be off! (low) coll. from ca. 1830. Since ca. 1840, gen. abbr. to Walker! . . . . Acc. to Bee, ex. John Walker, a prevaricating hook-nosed spy.