docs(rpn): fix inaccurate Stack() return value comment

The comment claimed Stack() returns nil for an empty stack, but
GetCurrentStack() uses slices.Clone() which preserves a non-nil empty
slice. Only returns nil if the internal currentStack pointer is nil,
which should not happen in normal usage.

1 files changed, 1 insertions, 1 deletions

diff --git a/internal/rpn/rpn_state.go b/internal/rpn/rpn_state.go
index 5797ebe..baf64de 100644
--- a/internal/rpn/rpn_state.go
+++ b/internal/rpn/rpn_state.go
@@ -96,7 +96,7 @@ func (r *RPN) SetCurrentStack(values []StackValue) {
 
 // Stack returns the current stack as a slice of StackValues.
 // This is a convenience wrapper around GetCurrentStack().
-// Returns nil if the stack is empty or nil.
+// Returns an empty slice if the stack has no values.
 func (r *RPN) Stack() []StackValue {
 	return r.GetCurrentStack()
 }