PartitionSpec 抛异常 Invalid partition spec.

[ChaomingZhangCN]

目前代码如下：

public PartitionSpec(String spec, boolean trim) {
    if (spec == null) {
      throw new IllegalArgumentException("Argument \'spec\' cannot be null");
    }
    String[] groups = spec.split("[,/]");
    for (String group : groups) {
      String[] kv = group.split("=");
      if (kv.length != 2) {
        throw new IllegalArgumentException("Invalid partition spec.");
      }

      String k = trim ? kv[0].trim() : kv[0];
      String v = (trim ? kv[1].trim() : kv[1])
          .replaceAll("'", "")
          .replaceAll("\"", "");
      if (k.length() == 0 || v.length() == 0) {
        throw new IllegalArgumentException("Invalid partition spec.");
      }

      set(k, v);
    }
  }

1. 对于 value 是空或者带 = 会报错，增加更友好的异常提示？
2. 是否需要将异常的 spec 放到异常里面，帮助排查问题