[Dubbo] Fix StringIndexOutOfBoundsException when len=0 #4402 (#4425)

* add guard clause for len=0

* add guard clause for len=0

Author: sunbufu

dubbo-common/src/main/java/org/apache/dubbo/common/io/Bytes.java

@@ -620,6 +620,9 @@ public static byte[] base642bytes(final String str, final int off, final int len
         if (len < 0) {
             throw new IndexOutOfBoundsException("base642bytes: length < 0, length is " + len);
         }
+        if (len == 0) {
+            return new byte[0];
+        }
         if (off + len > str.length()) {
             throw new IndexOutOfBoundsException("base642bytes: offset + length > string length.");
         }
@@ -708,6 +711,9 @@ public static byte[] base642bytes(final String str, final int off, final int len
         if (len < 0) {
             throw new IndexOutOfBoundsException("base642bytes: length < 0, length is " + len);
         }
+        if (len == 0) {
+            return new byte[0];
+        }
         if (off + len > str.length()) {
             throw new IndexOutOfBoundsException("base642bytes: offset + length > string length.");
         }

dubbo-common/src/test/java/org/apache/dubbo/common/io/BytesTest.java

@@ -57,6 +57,12 @@ public void testMain() throws Exception {
 
         byte[] bytesWithC64 = Bytes.base642bytes(str, C64);
         assertThat(bytesWithC64, is(bytes));
+
+        byte[] emptyBytes = Bytes.base642bytes("dubbo", 0, 0);
+        assertThat(emptyBytes, is("".getBytes()));
+
+        assertThat(Bytes.base642bytes("dubbo", 0, 0, ""), is("".getBytes()));
+        assertThat(Bytes.base642bytes("dubbo", 0, 0, new char[0]), is("".getBytes()));
     }
 
     @Test