ANTLR v4签名整数规则

Question

在minijava示例的ANTLR4语法中我想按照以下规则解析有符号整数：

IntegerLiteral:IntegerSign? DecimalIntegerLiteral;
fragment
DecimalIntegerLiteral:DecimalNumeral IntegertypeSuffix?;
fragment
IntegerSign:'+'|'-';
fragment
IntegertypeSuffix:[lL];
fragment
DecimalNumeral:'0'| NonZeroDigit(Digits?| Underscores Digits);
fragment
Digits:Digit(DigitsAndUnderscores? Digit)?;
fragment
Digit:'0'| NonZeroDigit;
fragment
NonZeroDigit:[1-9];
fragment
DigitsAndUnderscores:DigitOrUnderscore+;
fragment
DigitOrUnderscore:Digit| '_';
fragment
Underscores:'_'+;

但在解析时会因表达式规则而导致错误：

expression:expression PLUS expression # addExpression

我应该如何避免这种冲突？