Github user lw-lin commented on the issue:
https://github.com/apache/spark/pull/14118
Here are some findings as I dug a little:
1. Since https://github.com/databricks/spark-csv/pull/102(Jul, 2015), we
would cast `""` as `null` for all types other than strings. For strings, `""`
would still be `""`;
2. Then we had added `treatEmptyValuesAsNulls` in
https://github.com/databricks/spark-csv/pull/147(Sep, 2015), after which, `""`
would be `null` when `treatEmptyValuesAsNulls == true` and would be still `""`
otherwise;
3. Then we had added `nullValue` in
https://github.com/databricks/spark-csv/pull/224(Dec, 2015), so people could
specify some string like `"MISSING"` other than the default `""` to represent
null values.
Then after the above 1.2.3., we have the following, which seems reasonable
and is backward-compatible:
<table>
<tr>
<td align="center"></td>
<td align="center">(default) when <i>nullVale == ""</i></td>
<td align="center">when <i>nullValue == "MISSING"</i></td>
</tr>
<tr>
<td align="center">(default) when <i>treatEmptyValuesAsNulls ==
false</i></td>
<td align="center">"" would cast to ""</td>
<td align="center">"" would cast to ""</td>
</tr>
<tr>
<td align="center">when <i>treatEmptyValuesAsNulls == true</i></td>
<td align="center">"" would cast to null</td>
<td align="center">"" would cast to ""</td>
</tr>
</table>
However we don't have this `treatEmptyValuesAsNulls` in Spark 2.0. @falaki
would it be OK with you if I add it back?
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