Graph drawing doesn't work with name prefix

[muzimuzhi]

Brief outline of the bug

When name prefix (or name suffix) is set, graph drawing throws Lua error

...graphdrawing/lua/pgf/gd/interface/InterfaceToDisplay.lua:510: attempting to create edge between nodes c and a that are not in the graph
stack traceback:
	[C]: in function 'assert'
	...graphdrawing/lua/pgf/gd/interface/InterfaceToDisplay.lua:510: in function 'pgf.gd.interface.InterfaceToDisplay.createEdge'
	[\directlua]:1: in main chunk.
\pgfgdedge ...uaescapestring {\the \toks 1}', }) }
                                                  \endpgfinterruptpath }}\en...

Minimal working example (MWE)

% !TeX program = lualatex
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{graphs, graphdrawing}
\usegdlibrary{layered}

\begin{document}
% without graphdrawing
\tikz                \graph { {a,b} -> c }; % works
\tikz[name prefix=x] \graph { {a,b} -> c }; % works

% with graphdrawing
\tikz                \graph[layered layout] { {a,b} -> c }; % works
\tikz[name prefix=x] \graph[layered layout] { {a,b} -> c }; % lua error
\tikz[name prefix=x] \graph[layered layout, /tikz/name prefix=]
                       { {a,b} -> c };                      % works again
\end{document}

I don't speak Lua, but by adding print() to function InterfaceToDisplay.createEdge(), I find when the error is thrown,
see lines 482--484 below, head == 'c' and tail == 'a'. However the keys stored in table scope.node_names is xa, xb, xc. Hence both h and t are nil and the assert() fails.

pgf/tex/generic/pgf/graphdrawing/lua/pgf/gd/interface/InterfaceToDisplay.lua

Lines 475 to 495 in 247f1f0

	function InterfaceToDisplay.createEdge(tail, head, direction, height, binding_infos)
	-- Setup
	local scope = InterfaceCore.topScope()
	local binding = InterfaceCore.binding
	-- Does vertex already exist?
	local h = scope.node_names[head]
	local t = scope.node_names[tail]
	assert (h and t, "attempting to create edge between nodes that are not in the graph")
	-- Create Arc object
	local arc = scope.syntactic_digraph:connect(t, h)
	-- Create Edge object
	local edge = Edge.new {
	head = h,
	tail = t,
	direction = direction,
	options = get_current_options_table(height)
	}

[hmenke]

Probably \graph doesn't wrap node names in \tikz@pp@name{<name>}.