Read arrow NullVector

Author: Kopilov

dataframe-arrow/src/main/kotlin/org/jetbrains/kotlinx/dataframe/io/arrowReadingImpl.kt

@@ -13,6 +13,7 @@ import org.apache.arrow.vector.Float8Vector
 import org.apache.arrow.vector.IntVector
 import org.apache.arrow.vector.LargeVarBinaryVector
 import org.apache.arrow.vector.LargeVarCharVector
+import org.apache.arrow.vector.NullVector
 import org.apache.arrow.vector.SmallIntVector
 import org.apache.arrow.vector.TimeMicroVector
 import org.apache.arrow.vector.TimeMilliVector
@@ -172,6 +173,10 @@ private fun StructVector.values(range: IntRange): List<Map<String, Any?>?> = ran
     getObject(it)
 }
 
+private fun NullVector.values(range: IntRange): List<Any?> = range.map {
+    getObject(it)
+}
+
 private fun VarCharVector.values(range: IntRange): List<String?> = range.map {
     if (isNull(it)) {
         null
@@ -245,6 +250,7 @@ private fun readField(root: VectorSchemaRoot, field: Field, nullability: Nullabi
             is TimeStampMilliVector -> vector.values(range).withTypeNullable(field.isNullable, nullability)
             is TimeStampSecVector -> vector.values(range).withTypeNullable(field.isNullable, nullability)
             is StructVector -> vector.values(range).withTypeNullable(field.isNullable, nullability)
+            is NullVector -> vector.values(range).withTypeNullable(field.isNullable, nullability)
             else -> {
                 throw NotImplementedError("reading from ${vector.javaClass.canonicalName} is not implemented")
             }