give error message when installing method fails

This package

newPackage ("Foo", Headline => "foo", DebuggingMode => true)
LieAlgebra = new Type of HashTable
basis(ZZ,ZZ,LieAlgebra) := List => (x) -> opts -> {}
export "LieAlgebra"
beginDocumentation()
document {
     Key => {
	     (basis,ZZ,ZZ,LieAlgebra),
	  },
     Headline => "make a basis",
     }

gives this error

Foo.m2:6:1:(3):[7]: error: documentation key for 'basis(ZZ,ZZ,LieAlgebra)' encountered, but no method installed

There actually is a line of code that should install the method function, but the function provided accepts two arguments instead of three, so the method didn't get installed. An error should have been flagged at that point, earlier.