表达式校验问题

版本：5.4.3
值：{"a ": 20}
表达式：(a >30) (a < 50)

上述表达式调用AviatorEvaluator.validate()时不会报错，但运行时报错AviatorBoolean cannot be cast to AviatorFunction

其实就是表达式之间少了个运算符（比如&&、 ||），请问这类表达式为何不在validate时抛出异常？

Start at AviatorEvaluator.validate() and reproduce the issue with value {"a ": 20} and expression (a >30) (a < 50). Trace how adjacent expressions are parsed and validated; done means the missing operator is rejected during validation with a clear exception instead of failing only at runtime.

Written by the indexing model from the issue text.