FIX: NULL equality should be useable with any type.

integration_tests/comparisons_test.ucg

@@ -169,3 +169,13 @@ assert {
     ok = "foo" !~ "bar",
     desc = "\"foo\" !~ \"bar\"",
 };
+
+assert {
+    ok = NULL != 1,
+    desc = "Integers are comparable to null",
+};
+
+assert {
+    ok = NULL != "string",
+    desc = "Strings are comparable to null",
+};

src/build/ir.rs

@@ -109,6 +109,9 @@ impl Val {
                 error::ErrorType::TypeFail,
                 pos,
             )),
+            // EMPTY is always comparable for equality.
+            (&Val::Empty, _) => Ok(false),
+            (_, &Val::Empty) => Ok(false),
             (me, tgt) => Err(error::BuildError::new(
                 format!("Types differ for {}, {}", me, tgt),
                 error::ErrorType::TypeFail,