regex.PatternSyntaxException: Look-behind group does not have an obvious maximum,该怎么处理

String str = "abc,afda,fdadfae,fdaee,fdafda,efdaf";Matcher m = Pattern.compile("(?<=^(?:[^,]+,){5})[^,]+(?=\\b|,)").matcher(str);if(m.find()){    System.out.println(m.group(0));}

Exception in thread "main" java.util.regex.PatternSyntaxException: Look-behind group does not have an obvious maximum length near index 17(?<=^(?:[^,]+,){5})[^,]+(?=\b|,)                 ^    at java.util.regex.Pattern.error(Pattern.java:1713)    at java.util.regex.Pattern.group0(Pattern.java:2488)    at java.util.regex.Pattern.sequence(Pattern.java:1806)    at java.util.regex.Pattern.expr(Pattern.java:1752)    at java.util.regex.Pattern.compile(Pattern.java:1460)    at java.util.regex.Pattern.<init>(Pattern.java:1133)    at java.util.regex.Pattern.compile(Pattern.java:823)    at com.rmouse.TestMagicCard.main(TestMagicCard.java:37)