fixes concatImpl to add defaultValue to types when it's used.

Author: Jolanrensen

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/api/concat.kt

@@ -12,6 +12,7 @@ import org.jetbrains.kotlinx.dataframe.hasNulls
 import org.jetbrains.kotlinx.dataframe.impl.columns.guessColumnType
 import org.jetbrains.kotlinx.dataframe.impl.commonType
 import org.jetbrains.kotlinx.dataframe.impl.getListType
+import org.jetbrains.kotlinx.dataframe.impl.guessValueType
 import org.jetbrains.kotlinx.dataframe.nrow
 import kotlin.reflect.KType
 import kotlin.reflect.full.withNullability
@@ -54,7 +55,13 @@ internal fun <T> concatImpl(name: String, columns: List<DataColumn<T>?>, columnS
                 col.toList()
             } else {
                 val nrow = columnSizes[index]
-                if (!nulls && nrow > 0 && defaultValue == null) nulls = true
+                if (!nulls && nrow > 0 && defaultValue == null) {
+                    nulls = true
+                } else if (defaultValue != null) {
+                    types.add(
+                        guessValueType(sequenceOf(defaultValue))
+                    )
+                }
                 List(nrow) { defaultValue }
             }
         }

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/api/concat.kt

@@ -12,6 +12,7 @@ import org.jetbrains.kotlinx.dataframe.hasNulls
 import org.jetbrains.kotlinx.dataframe.impl.columns.guessColumnType
 import org.jetbrains.kotlinx.dataframe.impl.commonType
 import org.jetbrains.kotlinx.dataframe.impl.getListType
+import org.jetbrains.kotlinx.dataframe.impl.guessValueType
 import org.jetbrains.kotlinx.dataframe.nrow
 import kotlin.reflect.KType
 import kotlin.reflect.full.withNullability
@@ -54,7 +55,13 @@ internal fun <T> concatImpl(name: String, columns: List<DataColumn<T>?>, columnS
                 col.toList()
             } else {
                 val nrow = columnSizes[index]
-                if (!nulls && nrow > 0 && defaultValue == null) nulls = true
+                if (!nulls && nrow > 0 && defaultValue == null) {
+                    nulls = true
+                } else if (defaultValue != null) {
+                    types.add(
+                        guessValueType(sequenceOf(defaultValue))
+                    )
+                }
                 List(nrow) { defaultValue }
             }
         }