fix: validate regex pattern at convert time so invalid or null patterns fall back to Spark

When routing RLike through the JVM UDF, reject Literal(null) and patterns
that fail Pattern.compile during planning. Both cases now produce withInfo
+ None, letting Spark evaluate the expression instead of crashing the
executor task with PatternSyntaxException or NullPointerException.

Author: andygrove

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

@@ -316,7 +316,19 @@ object CometRLike extends CometExpressionSerde[RLike] {
       inputs: Seq[Attribute],
       binding: Boolean): Option[Expr] = {
     expr.right match {
-      case Literal(_, DataTypes.StringType) =>
+      case Literal(value, DataTypes.StringType) =>
+        if (value == null) {
+          withInfo(expr, "Null literal pattern is handled by Spark fallback")
+          return None
+        }
+        val patternStr = value.toString
+        try {
+          java.util.regex.Pattern.compile(patternStr)
+        } catch {
+          case e: java.util.regex.PatternSyntaxException =>
+            withInfo(expr, s"Invalid regex pattern: ${e.getDescription}")
+            return None
+        }
         val subjectProto = exprToProtoInternal(expr.left, inputs, binding)
         val patternProto = exprToProtoInternal(expr.right, inputs, binding)
         if (subjectProto.isEmpty || patternProto.isEmpty) {