fix

Author: hengyunabc

core/src/main/java/com/taobao/arthas/core/util/RegexCacheManager.java

@@ -29,7 +29,7 @@ public static RegexCacheManager getInstance() {
      * 获取正则表达式Pattern对象，优先从缓存获取，缓存未命中则编译并缓存
      */
     public Pattern getPattern(String regex) {
-        if (regex == null || regex.isEmpty()) {
+        if (regex == null) {
             return null;
         }
 

core/src/test/java/com/taobao/arthas/core/util/RegexCacheManagerTest.java

@@ -49,7 +49,10 @@ public void testBasicCacheFunctionality() {
         Assert.assertNull(nullPattern);
 
         Pattern emptyPattern = cacheManager.getPattern("");
-        Assert.assertNull(emptyPattern);
+        Assert.assertNotNull(emptyPattern);
+        Assert.assertTrue(emptyPattern.matcher("").matches());
+        Assert.assertFalse(emptyPattern.matcher("non-empty").matches());
+        Assert.assertEquals(3, cacheManager.getCacheSize());
     }
 
     /**

core/src/test/java/com/taobao/arthas/core/util/matcher/RegexMatcherTest.java

@@ -16,6 +16,12 @@ public void testMatchingWithNullInputs(){
         Assert.assertTrue(new RegexMatcher("foobar").matching("foobar"));
     }
 
+    @Test
+    public void testMatchingWithEmptyPattern() {
+        Assert.assertTrue(new RegexMatcher("").matching(""));
+        Assert.assertFalse(new RegexMatcher("").matching("foobar"));
+    }
+
     /**
      * test regux with . | * + ? \s \S \w \W and so on...
      */