[improvement](chat) Fix get metrics error in queryReqConverter (#547)

common/src/main/java/com/tencent/supersonic/common/util/jsqlparser/SqlParserSelectHelper.java

@@ -289,6 +289,7 @@ public class SqlParserSelectHelper {
         Set<FieldExpression> orderByFieldExpressions = getOrderByFields(plainSelect);
         Set<String> collect = orderByFieldExpressions.stream()
                 .map(fieldExpression -> fieldExpression.getFieldName())
+                .filter(Objects::nonNull)
                 .collect(Collectors.toSet());
         result.addAll(collect);
     }

common/src/test/java/com/tencent/supersonic/common/util/jsqlparser/SqlParserSelectHelperTest.java

@@ -170,6 +170,11 @@ class SqlParserSelectHelperTest {
                 + "WHERE MONTH(数据日期) = 9) FROM 营销 WHERE 国家中文名 = '中国' AND MONTH(数据日期) = 9");
 
         Assert.assertEquals(allFields.size(), 3);
+
+        allFields = SqlParserSelectHelper.getAllFields(
+                "SELECT 用户, 页面  FROM 超音数用户部门 GROUP BY 用户, 页面 ORDER BY count(*) DESC");
+
+        Assert.assertEquals(allFields.size(), 2);
     }
 
     @Test