A function can only return one value. As soon as "Underweight" is returned the functions stops executing and the statements further down are not evaluated.

the constraints are stated as beteen 1 and 12, therefore the solution does not need to account for negative numbers

Please use spoiler flag next time, your post was visible in the homepage.

you are wrong. Only 1 "if" will return a value here.

no me gusta esta solucion, porque si el mes es 2 abria tendria que devolver 1,2 , 3 y 4. ya que 2 es un mes menor a 12, a 9, a 6 y a 3. y la idea es devolver 1 mes, corrijanmen si me equivoco

Why did we need to return null

The input will always be in lowercase and never be empty.

Won't happen.

the code won't work

what if A string is given in uppperCase

Thank you