Line Protocol: Empty tag value gets converted to a format rejected by InfluxDB server 0.9.1

A tag in JSON doc as follows:

```
{
    "tags" : {
        "my_tag" : ""
    }
}
```

is converted to line format, by line_protocol.py:make_lines(), as:
my_tag=

This resulted in format error when sent to InfluxDB server.  Should the method convert it to the following instead?
my_tag=""

Or should I simply omit empty tag?

Please advise.
