HyukjinKwon opened a new pull request, #36435:
URL: https://github.com/apache/spark/pull/36435

   ### What changes were proposed in this pull request?
   
   This PR is a followup of https://github.com/apache/spark/pull/33436 that 
adds a legacy configuration. It's found that that it can break a valid usacase 
(https://github.com/apache/spark/pull/33436/files#r863271189):
   
   ```scala
   import org.apache.spark.sql.types._
   val ds = Seq("a,", "a,b").toDS
   spark.read.schema(
     StructType(
       StructField("f1", StringType, nullable = false) ::
       StructField("f2", StringType, nullable = false) :: Nil)
     ).option("mode", "FAILFAST").csv(ds).show()
   ```
   
   **Before:**
   
   ```
   +---+---+
   | f1| f2|
   +---+---+
   |  a|  b|
   +---+---+
   ```
   
   **After:**
   
   ```
   +---+----+
   | f1|  f2|
   +---+----+
   |  a|null|
   |  a|   b|
   +---+----+
   ```
   
   ### Why are the changes needed?
   
   To avoid breakage of valid usecases.
   
   ### Does this PR introduce _any_ user-facing change?
   
   Yes, it adds a new configuration 
`spark.sql.legacy.respectNullabilityInTextDatasetConversion` (`false` by 
default) to respect the nullability in 
`DataFrameReader.schema(schema).csv(dataset)` and 
`DataFrameReader.schema(schema).json(dataset)` when the user-specified schema 
is provided.
   
   ### How was this patch tested?
   
   Unittests were added.


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