fix from dubbo:master, 2.5.7 : GenericJSONConverter主要是用在日志部分输出，所以当我们输出locale对象时就发生stack溢出。
```
java.lang.StackOverflowError
	at com.alibaba.dubbo.common.json.JSONWriter.valueString(JSONWriter.java:189)
	at com.alibaba.dubbo.common.json.GenericJSONConverter$7.encode(GenericJSONConverter.java:100)
	at com.alibaba.dubbo.common.json.GenericJSONConverter.writeValue(GenericJSONConverter.java:338)
	at com.alibaba.dubbo.common.json.GenericJSONConverter.writeValue(GenericJSONConverter.java:347)
	at com.alibaba.dubbo.common.json.GenericJSONConverter.writeValue(GenericJSONConverter.java:395)
	at com.alibaba.dubbo.common.json.GenericJSONConverter.writeValue(GenericJSONConverter.java:347)
	at com.alibaba.dubbo.common.json.GenericJSONConverter.writeValue(GenericJSONConverter.java:395)
```
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package com.alibaba.dubbo.common.json;
import com.alibaba.dubbo.common.bytecode.Wrapper;
import com.alibaba.dubbo.common.io.Bytes;
import java.io.IOException;
import java.lang.reflect.Array;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Collection;
import java.util.Date;
import java.util.HashMap;