fix bug and add test

hutool-core/src/main/java/cn/hutool/core/collection/iter/FilterIter.java

@@ -84,7 +84,7 @@ public class FilterIter<E> implements Iterator<E> {
 	private boolean setNextObject() {
 		while (iterator.hasNext()) {
 			final E object = iterator.next();
-			if (null != filter && filter.test(object)) {
+			if (null == filter || filter.test(object)) {
 				nextObject = object;
 				nextObjectSet = true;
 				return true;

hutool-core/src/test/java/cn/hutool/core/collection/iter/FilterIterTest.java

@@ -0,0 +1,23 @@
+package cn.hutool.core.collection.iter;
+
+import cn.hutool.core.collection.ListUtil;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.Iterator;
+
+public class FilterIterTest {
+
+	@Test
+	public void iterNullTest(){
+		final Iterator<String> it = ListUtil.of("1", "2").iterator();
+		final FilterIter<String> filterIter = new FilterIter<>(it, null);
+		int count = 0;
+		while (filterIter.hasNext()) {
+			if(null != filterIter.next()){
+				count++;
+			}
+		}
+		Assert.assertEquals(2, count);
+	}
+}