Fix issue with uninitialized _param in recursive functions with unit argument.

Fixes #6719

Author: cristianoc

CHANGELOG.md

@@ -21,6 +21,7 @@
 - Avoid generating calls to Curry when adjusting arity of uncurried functions. https://github.com/rescript-lang/rescript-compiler/pull/6870
 - Fix build after calling without `-warn-error`, see https://github.com/rescript-lang/rescript-compiler/issues/6868 for more details. https://github.com/rescript-lang/rescript-compiler/pull/6877
 - Fix `Js.Types.JSBigInt` payload to use native `bigint` type. https://github.com/rescript-lang/rescript-compiler/pull/6911
+- Fix issue with uninitialized `_param` in recursive functions with unit argument. https://github.com/rescript-lang/rescript-compiler/pull/6907
 
 # 11.1.3-rc.1
 

jscomp/core/lam_compile.ml

@@ -328,6 +328,7 @@ and compile_recursive_let ~all_bindings (cxt : Lam_compile_context.t)
          ]}
           [Alias] may not be exact
       *)
+      let params = if oneUnitArg then [] else params in
       let ret : Lam_compile_context.return_label =
         {
           id;