为提高效率，提问时请提供以下信息，问题描述清晰可优先响应。
【DM版本】:8.1.2.141
【操作系统】：linux
【CPU】:x86
【问题描述】*：
两条数据的手机号字段都为空，执行insert语句，结果触发了唯一索引phone_bumber_index。

CREATE TABLE "iam"."user"
(
"id" BIGINT NOT NULL,
"name" VARCHAR(64 CHAR),
"phone_number" VARCHAR(20 CHAR),
"tenant_id" VARCHAR(64 CHAR) NOT NULL,
CONSTRAINT "user_PRIMARY" NOT CLUSTER PRIMARY KEY("id"),
CONSTRAINT "phone_bumber_index" UNIQUE("phone_number", "tenant_id")) STORAGE(ON "MAIN", CLUSTERBTR) ;

INSERT INTO "iam"."user" ("id","name","phone_number","tenant_id") VALUES (1,'张三',null,'1');
INSERT INTO "iam."user" ("id","name","phone_number","tenant_id") VALUES (2,'李四',null,'1');