proxy.pathsuffix value empty

[asif_aftab]

<PreFlow name="PreFlow">
<Request>
<Step>
<Name>JSC.Test</Name>
</Step>
</Request>
<Response/>
</PreFlow>

my js content 

print(context.getVariable("proxy.pathsuffix"));
print('proxy.pathsuffix', context.getVariable('proxy.pathsuffix'));

but output is

proxy.pathsuffix

getting empty value