diff --git a/src/main/java/xyz/zhouxy/plusone/validator/BaseValidator.java b/src/main/java/xyz/zhouxy/plusone/validator/BaseValidator.java
index e0bcae4..93c2e7d 100644
--- a/src/main/java/xyz/zhouxy/plusone/validator/BaseValidator.java
+++ b/src/main/java/xyz/zhouxy/plusone/validator/BaseValidator.java
@@ -93,7 +93,7 @@ public class BaseValidator<T> {
             this.getter = getter;
         }
 
-        <E extends RuntimeException> void withRule(Predicate<PROPERTY> condition,
+        <E extends RuntimeException> void withRule(Predicate<? super PROPERTY> condition,
                 Function<PROPERTY, E> exceptionCreator) {
             withRule(value -> {
                 if (!condition.test(value)) {
@@ -167,22 +167,22 @@ public class BaseValidator<T> {
 
         // ===== isTrue =====
 
-        public THIS isTrue(Predicate<PROPERTY> condition) {
+        public THIS isTrue(Predicate<? super PROPERTY> condition) {
             return isTrue(condition, "无效的用户输入");
         }
 
-        public THIS isTrue(Predicate<PROPERTY> condition, String errMsg) {
+        public THIS isTrue(Predicate<? super PROPERTY> condition, String errMsg) {
             return isTrue(condition, convertExceptionCreator(errMsg));
         }
 
         public <E extends RuntimeException> THIS isTrue(
-                Predicate<PROPERTY> condition,
+                Predicate<? super PROPERTY> condition,
                 Supplier<E> exceptionCreator) {
             return isTrue(condition, convertExceptionCreator(exceptionCreator));
         }
 
         public <E extends RuntimeException> THIS isTrue(
-                Predicate<PROPERTY> condition,
+                Predicate<? super PROPERTY> condition,
                 Function<PROPERTY, E> exceptionCreator) {
             withRule(condition, exceptionCreator);
             return thisObject();
diff --git a/src/test/java/xyz/zhouxy/plusone/map/MapValidatorTests.java b/src/test/java/xyz/zhouxy/plusone/map/MapValidatorTests.java
index 0f90d14..aba5fdf 100644
--- a/src/test/java/xyz/zhouxy/plusone/map/MapValidatorTests.java
+++ b/src/test/java/xyz/zhouxy/plusone/map/MapValidatorTests.java
@@ -6,8 +6,10 @@ import java.util.Map;
 import java.util.Objects;
 import java.util.regex.Pattern;
 
+import org.apache.commons.lang3.StringUtils;
 import org.junit.jupiter.api.Test;
 
+import xyz.zhouxy.plusone.commons.util.Predicates;
 import xyz.zhouxy.plusone.constant.Patterns;
 import xyz.zhouxy.plusone.validator.MapValidator;
 
@@ -42,7 +44,8 @@ class TestValidator extends MapValidator {
     TestValidator() {
         super(Arrays.asList(USERNAME, ACCOUNT, PASSWORD, AGE, BOOLEAN, ROLE_LIST));
         this.ruleForString(USERNAME)
-                .notEmpty()
+                .isTrue(Predicates.of(StringUtils::isNotEmpty)
+                        .and(Objects::nonNull))
                 .matches(Patterns.USERNAME.getPattern(),
                         username -> new IllegalArgumentException(String.format("用户名【%s】不符合规范", username)));
         this.ruleForString(ACCOUNT)