When 'lack' is used as a noun, 'lack of/in' are used the way like this; A problem of this are is a lack of food supply. (a lack of something = being poor in something) Food supply is a lack in this area. (a lack = a thing wanted)
When "lack" is a noun, you say "a lack of something"; When "lack" is a verb, you say "lack something"; When "lack" changes into an adjective form of "lacking," you say "I'm lacking in something."