Can you have curving, empty, broken arrows in xymatrix?

Question

In \xymatrix, the command
\ar@{}[dr] |{\text{lab}}
typesets an empty arrow, broken by some text. Similarly, the command
\ar@/^10pt/ @{->}[ur] |{\text{lab}}
typesets a curving arrow, broken by some text. I would expect
\ar@/^10pt/ @{}[ur] |{\text{lab}}
then to typset a curving, empty arrow, broken by some text, but it doesn't. Is there a convenient way to achieve curving, empty, broken?

Here is a minimal example:

\documentclass{amsart}  
\usepackage[all]{xy}  
\begin{document}  
\begin{equation}  
\xymatrix{  
a \ar@/^10pt/ @{}[r] |{\text{lab}} & b  
}  
\end{equation}  
\end{document}

Answer 1

I don't know why this happens, but replacing \ar@{} by \ar@{{ }{ }} or \ar@{ { }} works. But \ar@{{ } } does not :). A minimal working example:

\documentclass{amsart}
\usepackage[all]{xy}
\begin{document}
\xymatrix{a \ar @{{ }{ }} @/^10pt/ [r] |{\text{lab}} & b}
\end{document}

If someone knows why this happens, edit me. My guess is that being more explicit to xy helps it.