removing erroneous use of TODO from zero() function, plus small QOL cleanup

Author: Jolanrensen

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

@@ -121,7 +121,7 @@ internal fun <T> Iterable<T>.anyNull(): Boolean = any { it == null }
 internal fun emptyPath(): ColumnPath = ColumnPath(emptyList())
 
 @PublishedApi
-internal fun <T : Number> KClass<T>.zero(): T =
+internal fun <T : Number> KClass<T>.zeroOrNull(): T? =
     when (this) {
         Int::class -> 0 as T
         Byte::class -> 0.toByte() as T
@@ -131,10 +131,14 @@ internal fun <T : Number> KClass<T>.zero(): T =
         Float::class -> 0.toFloat() as T
         BigDecimal::class -> BigDecimal.ZERO as T
         BigInteger::class -> BigInteger.ZERO as T
-        Number::class -> 0 as T
-        else -> TODO()
+        Number::class -> 0 as? T
+        else -> null
     }
 
+@PublishedApi
+internal fun <T : Number> KClass<T>.zero(): T =
+    zeroOrNull() ?: throw NotImplementedError("Zero value for $this is not supported")
+
 internal fun <T> catchSilent(body: () -> T): T? =
     try {
         body()