A null parameter has been passed for month function

You need to first check that the date you are passing in month() is not null, add an if condition to it.

if(
  isnull(fv!item.asDate),
  false,
  month(fv!item.asDate) = local!month
)

Please don't use isnull(). It was never a safe option. Instead, go for a!isnullorempty() should cover more usecases. 

if(
a!isnullOrEmpty(index(fv!item, "asDate", null)),
false,
contains(
tointeger(local!month),
month(index(fv!item, "asDate", null))
)
)

I already used that one, but it's not resolved, bcz same error occurred. plz suggest another way

if(
a!isnullOrEmpty(index(fv!item, "asDate", null)),
false,
contains(
tointeger(local!month),
month(index(fv!item, "asDate", null))
)
)

I already used that one, but it's not resolved, bcz same error occurred. plz suggest another way