fix(report): 修复关键行为评估报告查询插件中的CASE表达式

- 将CASE表达式的ELSE部分从null改为空字符串，避免数据库查询异常
- 修正了项目编号匹配时的结果字段处理逻辑

code/hr/nckd-jxccl-hr/src/main/java/nckd/jxccl/hr/psms/plugin/form/other/report/KeyBeHavEvalReptQueryPlugin.java

@@ -246,7 +246,7 @@ public class KeyBeHavEvalReptQueryPlugin extends AbstractReportListDataPlugin im
         List<String> columnFieldNames = new ArrayList<>();
         for (String projectNumber : projectNumbers) {
             String caseExpression = String.format(
-                "CASE WHEN %s = '%s' THEN %s ELSE null END",
+                "CASE WHEN %s = '%s' THEN %s ELSE '' END",
                 PROJECT_NUMBER_FIELD,
                 projectNumber,
                 RESULT_FIELD