fix null bug

hutool-core/src/main/java/cn/hutool/core/net/url/UrlBuilder.java

@@ -371,9 +371,10 @@ public final class UrlBuilder implements Builder<String> {
 	}
 
 	/**
-	 * 获取查询语句，例如a=1&amp;b=2
+	 * 获取查询语句，例如a=1&amp;b=2<br>
+	 * 可能为{@code null}
 	 *
-	 * @return 查询语句，例如a=1&amp;b=2
+	 * @return 查询语句，例如a=1&amp;b=2，可能为{@code null}
 	 */
 	public UrlQuery getQuery() {
 		return query;

hutool-core/src/test/java/cn/hutool/core/net/UrlBuilderTest.java

@@ -139,6 +139,13 @@ public class UrlBuilderTest {
 		Assert.assertEquals("frag1", builder.getFragment());
 	}
 
+	@Test
+	public void ofNullQueryTest() {
+		final UrlBuilder builder = UrlBuilder.of("http://www.hutool.cn/aaa/bbb", CharsetUtil.CHARSET_UTF_8);
+		Assert.assertNotNull(builder.getQuery());
+		Assert.assertNull(builder.getQuery().get("a"));
+	}
+
 	@Test
 	public void ofWithChineseTest() {
 		final UrlBuilder builder = UrlBuilder.ofHttp("www.hutool.cn/aaa/bbb/?a=张三&b=%e6%9d%8e%e5%9b%9b#frag1", CharsetUtil.CHARSET_UTF_8);