[antlr-interest] How to walk a tree with an imaginary root

[=?gb2312?q?=CB=EF=BC=CD=B8=D5=20Jigang=20(Robert)=20Sun?=]

Hi all,

In parser, to build a tree,

ruleAlt!
    :
    l:graph {##=#([RULE_ALT,"ruleAlt"],l);}
    ;

In tree walker,

ruleAlt
    :     
    RULE_ALT graph 
    ;

got a tree has only "ruleAlt" node without any child, 
runtime error: <AST>: unexpected end of subtree.

Could you help?

Jigang


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