[antlr-interest] RewriteEmptyStreamException when changing from quoted string to token?

[Jon Schewe]

I have the following parser rule and lexer rule (others exist as well). 
I'm using antlr 3.0.1.  If I change '*' in multExpr to PRODUCT then at
runtime I get an exception.  If I leave it at '*', all is fine.  What am
I doing wrong here?
   [junit] token PRODUCT
    [junit] org.antlr.runtime.tree.RewriteEmptyStreamException: token
PRODUCT
    [junit]     at
org.antlr.runtime.tree.RewriteRuleElementStream._next(RewriteRuleElementStream.java:158)
    [junit]     at
org.antlr.runtime.tree.RewriteRuleTokenStream.next(RewriteRuleTokenStream.java:57)
 

/**
 * @param negate if true, negate all expressions by multiplying by -1
 */   
multExpr[boolean negate]
    :   atom ('*' atom)* -> {negate}? ^(PRODUCT ^(NUMBER DOUBLE["-1"])
atom+)
                             ->           ^(PRODUCT atom+)
    ;

PRODUCT         :   '*'     ;

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Jon Schewe | http://mtu.net/~jpschewe
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