public static int getFluidId(FluidStack stack) {
    if (stack == null)
        return -1;
    if (stack.getFluid() == null)
        return -1;
    return FluidRegistry.getFluidID(stack.getFluid().getName());
}

Replace the following:

fluidStack.getFluidID()

With the following:

[class with above code].getFluidId(fluidStack)

Yours at the cost of four easy payments of NONE!

Just update forge; how hard can it be :P

I honestly don't think there's much need for this... Seems like added fluff for a version that isn't existent anymore.

The version in question is still "recommended". Support it as long as it is.

There are mods which don't have updated fluid handling, like Growthcraft. You're welcome to update them manually (and get a lawyer because they're closed source or they would be updated already - unless it's possible to override such a method with reflection, in which case explanation would be highly welcome) or provide an equal alternative, with rice paddies, barrels, ropes, hops and grape vines, et cetera in Growthcraft's case.

P.S. And to think it all could be avoided if KingLemming just did a proper thing and added getFluidID() a few builds before he changed fluid handling so that newer handling would essentially have built-in backwards compatibility for said few builds.

In short terms...close this cause it's obsolete. --Either use the correct Forge version or downgrade BM