feat: implement native empty2null spark inner function

spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala

@@ -256,7 +256,8 @@ object QueryPlanSerde extends Logging with CometExprShim with CometTypeShim {
       classOf[ToCharacter] -> CometToCharacter,
       classOf[ToNumber] -> CometToNumber,
       classOf[TryToNumber] -> CometTryToNumber,
-      classOf[Mask] -> CometMask)
+      classOf[Mask] -> CometMask,
+      classOf[Empty2Null] -> CometEmpty2Null)
     base ++ sparkVersionSpecificStringExpressions
   }
 

spark/src/main/scala/org/apache/comet/serde/strings.scala

@@ -19,7 +19,7 @@
 
 package org.apache.comet.serde
 
-import org.apache.spark.sql.catalyst.expressions.{Attribute, BitLength, Cast, Concat, ConcatWs, Elt, Expression, FindInSet, FormatNumber, FormatString, GetJsonObject, If, InitCap, IsNull, Left, Length, Levenshtein, Like, Literal, Lower, Mask, OctetLength, Overlay, RegExpExtract, RegExpExtractAll, RegExpInStr, RegExpReplace, Right, RLike, SoundEx, StringLocate, StringLPad, StringRepeat, StringReplace, StringRPad, StringSplit, StringTranslate, Substring, SubstringIndex, ToCharacter, ToNumber, TryToNumber, UnBase64, Upper}
+import org.apache.spark.sql.catalyst.expressions.{Attribute, BitLength, Cast, Concat, ConcatWs, Elt, Empty2Null, Expression, FindInSet, FormatNumber, FormatString, GetJsonObject, If, InitCap, IsNull, Left, Length, Levenshtein, Like, Literal, Lower, Mask, OctetLength, Overlay, RegExpExtract, RegExpExtractAll, RegExpInStr, RegExpReplace, Right, RLike, SoundEx, StringLocate, StringLPad, StringRepeat, StringReplace, StringRPad, StringSplit, StringTranslate, Substring, SubstringIndex, ToCharacter, ToNumber, TryToNumber, UnBase64, Upper}
 import org.apache.spark.sql.types.{BinaryType, DataTypes, LongType, StringType}
 import org.apache.spark.unsafe.types.UTF8String
 
@@ -647,3 +647,7 @@ object CometToNumber extends CometCodegenDispatch[ToNumber]
 object CometTryToNumber extends CometCodegenDispatch[TryToNumber]
 
 object CometMask extends CometCodegenDispatch[Mask]
+
+// A internal function that converts the empty string to null for partition values.
+// This function should be only used in V1Writes.
+object CometEmpty2Null extends CometCodegenDispatch[Empty2Null]