title: ANTLR "unexpected end of subtree"
body: <p>Hey. I'm new to ANTLR. ANTLRWorks wizard wrrited for me the following code:</p>
  
  <pre><code>grammar test;
  
  ID  :   ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'_')*
      ;
  
  INT :   '0'..'9'+
      ;
  
  FLOAT
      :   ('0'..'9')+ '.' ('0'..'9')* EXPONENT?
      |   '.' ('0'..'9')+ EXPONENT?
      |   ('0'..'9')+ EXPONENT
      ;
  
  COMMENT
      :   '//' ~('\n'|'\r')* '\r'? '\n' {$channel=HIDDEN;}
      |   '/*' ( options {greedy=false;} : . )* '*/' {$channel=HIDDEN;}
      ;
  
  WS  :   ( ' '
          | '\t'
          | '\r'
          | '\n'
          ) {$channel=HIDDEN;}
      ;
  
  STRING
      :  '"' ( ESC_SEQ | ~('\\'|'"') )* '"'
      ;
  CHAR:  '\'' ( ESC_SEQ | ~('\''|'\\') ) '\''
      ;
  
  fragment
  EXPONENT : ('e'|'E') ('+'|'-')? ('0'..'9')+ ;
  
  fragment
  HEX_DIGIT : ('0'..'9'|'a'..'f'|'A'..'F') ;
  
  fragment
  ESC_SEQ
      :   '\\' ('b'|'t'|'n'|'f'|'r'|'\"'|'\''|'\\')
      |   UNICODE_ESC
      |   OCTAL_ESC
      ;
  
  fragment
  OCTAL_ESC
      :   '\\' ('0'..'3') ('0'..'7') ('0'..'7')
      |   '\\' ('0'..'7') ('0'..'7')
      |   '\\' ('0'..'7')
      ;
  
  fragment
  UNICODE_ESC
      :   '\\' 'u' HEX_DIGIT HEX_DIGIT HEX_DIGIT HEX_DIGIT
      ;
  </code></pre>
  
  <p>When debugging it, it throws the following error:</p>
  
  <pre><code>[22:45:49] error(100): C:\Documents and Settings\user\Desktop\test.g:0:0: syntax error: codegen: &lt;AST&gt;:0:0: unexpected end of subtree
  </code></pre>
  
  <p>Can someone explain me what is the error, where is it and how can I fix it?</p>
  
  <p>Thanks.</p>