Github user aa8y commented on a diff in the pull request:
https://github.com/apache/spark/pull/20068#discussion_r159160508
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVOptions.scala
---
@@ -152,7 +152,11 @@ class CSVOptions(
writerSettings.setIgnoreLeadingWhitespaces(ignoreLeadingWhiteSpaceFlagInWrite)
writerSettings.setIgnoreTrailingWhitespaces(ignoreTrailingWhiteSpaceFlagInWrite)
writerSettings.setNullValue(nullValue)
- writerSettings.setEmptyValue(nullValue)
+ // The Univocity parser parses empty strings as `null` by default.
This is the default behavior
+ // for Spark too, since `nullValue` defaults to an empty string and
has a higher precedence to
+ // setEmptyValue(). But when `nullValue` is set to a different value,
that would mean that the
+ // empty string should be parsed not as `null` but as an empty string.
+ writerSettings.setEmptyValue("")
--- End diff --
I talked about this with Hyukjin Kwon before. I think the previous behavior
should _not_ be exposed as an option as the previous behavior was a bug. All it
did was that it _always_ coerced empty values to `null`s. If the `nullValue`
was not set, then the it was set to `""` by default which coerced `""` to
`null`. The empty value being set to `""` had no affect in this case. If it was
set to something else, say `\N`, then the empty value was also set to `\N`
which resulted in parsing both `\N` and `""` to `null`, as `""` was no longer
considered as an empty value and the `""` being coerced to null is the
Univocity parser's default.
Setting empty value explicitly to the `""` literal would ensure that an
empty string is always parsed as empty string, unless `nullValue` is not set or
it is set to `""`, which is what people would do if they want `""` to be parsed
as `null`, which would be the old behavior.
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