Set values of empty strings in read and in write

Author: MaxGekk

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVOptions.scala

@@ -164,7 +164,7 @@ class CSVOptions(
     writerSettings.setIgnoreLeadingWhitespaces(ignoreLeadingWhiteSpaceFlagInWrite)
     writerSettings.setIgnoreTrailingWhitespaces(ignoreTrailingWhiteSpaceFlagInWrite)
     writerSettings.setNullValue(nullValue)
-    writerSettings.setEmptyValue(nullValue)
+    writerSettings.setEmptyValue("\"\"")
     writerSettings.setSkipEmptyLines(true)
     writerSettings.setQuoteAllFields(quoteAll)
     writerSettings.setQuoteEscapingEnabled(escapeQuotes)
@@ -185,6 +185,7 @@ class CSVOptions(
     settings.setInputBufferSize(inputBufferSize)
     settings.setMaxColumns(maxColumns)
     settings.setNullValue(nullValue)
+    settings.setEmptyValue("")
     settings.setMaxCharsPerColumn(maxCharsPerColumn)
     settings.setUnescapedQuoteHandling(UnescapedQuoteHandling.STOP_AT_DELIMITER)
     settings