Do not add redundant checks for nil values

compiler-core/src/javascript/decision.rs

···
                     // We never generate runtime checks for tuples, so we skip
                     // those altogether here.
                     RuntimeCheck::Tuple { .. } => None,
+                    RuntimeCheck::Variant { .. } if variable.type_.is_nil() => None,
                     _ => self
                         .variables
                         .runtime_check(variable, check, CheckNegation::Negated)
···
                     (_, CheckNegation::NotNegated) => docvec!["!", value, ".isOk()"],
                     (_, CheckNegation::Negated) => docvec![value, ".isOk()"],
                 }
-            }
-
-            // Checking that a value typed as `Nil` is not `Nil` is always going
-            // fail.
-            RuntimeCheck::Variant { .. } if variable.type_.is_nil() && negation.is_negated() => {
-                "false".to_doc()
             }
 
             RuntimeCheck::Variant { match_, .. } => {

compiler-core/src/javascript/tests/assert.rs

···
 "#
     );
 }
+
+#[test]
+fn assert_nil_always_throws() {
+    assert_js!(
+        r#"
+pub fn go(x: Nil) {
+  let assert Nil = x
+}
+"#
+    );
+}

compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__assert__assert_nil_always_throws.snap

···
+---
+source: compiler-core/src/javascript/tests/assert.rs
+expression: "\npub fn go(x: Nil) {\n  let assert Nil = x\n}\n"
+---
+----- SOURCE CODE
+
+pub fn go(x: Nil) {
+  let assert Nil = x
+}
+
+
+----- COMPILED JAVASCRIPT
+export function go(x) {
+  
+  return x;
+}

compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__blocks__let_assert_message_no_lifted.snap

···
 
 export function main() {
   let $ = side_effects(new Ok(10));
-  if ($.isOk() || false) {
+  if ($.isOk()) {
     throw makeError(
       "let_assert",
       "my/mod",