seq.max(coll) 存在报 NullPointerException 的问题

【问题描述】
当指定的集合中存在 null 元素，且 null 位于集合的首位时，会抛出 NullPointerException。

【测试步骤】
```
Expression expr = AviatorEvaluator.compile("seq.max(coll)");
Map env = new HashMap<>();
env.put("coll", Arrays.asList(null, 1, 2));
Object obj = expr.execute(env);
System.out.println(obj);
```

【预期结果】
忽略集合中的 null 值，输出结果为 2

【实际结果】
报错 NullPointerException

Start by reproducing the reported seq.max(coll) expression with Arrays.asList(null, 1, 2) and inspect the seq.max implementation or entry point. Done means null elements are ignored and the expression returns 2 without throwing a NullPointerException.

Written by the indexing model from the issue text.