message: Change "may never" to "must never"
  "may never" indicates that it's allowed to never hold a value. I believe the intent here is that it is not allowed to ever hold a value.
diff: @@ -253,7 +253,7 @@ protected:
  /// everywhere.
  /// A ValueHandle can have 3 states:
  /// 1. null state (empty type and empty value), in which case it does not hold
  -/// a value and may never hold a Value (not now of in the future). This is
  +/// a value and must never hold a Value (now or in the future). This is
  /// used for MLIR operations with zero returns as well as the result of
  /// calling a NestedBuilder::operator(). In both cases the objective is to
  /// have an object that can be inserted in an ArrayRef<ValueHandle> to
  