Adding back a null check for SparkFileWriterFactory.schema

Author: pvary

spark/v4.0/spark/src/main/java/org/apache/iceberg/spark/source/SparkFileWriterFactory.java

@@ -95,7 +95,7 @@ class SparkFileWriterFactory extends RegistryBasedFileWriterFactory<InternalRow,
         equalityDeleteSortOrder,
         writeProperties,
         calculateSparkType(dataSparkType, dataSchema),
-        calculateSparkType(equalityDeleteSparkType, equalityDeleteRowSchema));
+        calculateSparkTypeForEqualityDelete(equalityDeleteSparkType, equalityDeleteRowSchema));
 
     this.table = table;
     this.format = dataFileFormat;
@@ -348,6 +348,16 @@ SparkFileWriterFactory build() {
   }
 
   private static StructType calculateSparkType(StructType sparkType, Schema schema) {
+    if (sparkType != null) {
+      return sparkType;
+    } else {
+      Preconditions.checkNotNull(schema, "Data schema must not be null");
+      return SparkSchemaUtil.convert(schema);
+    }
+  }
+
+  private static StructType calculateSparkTypeForEqualityDelete(
+      StructType sparkType, Schema schema) {
     if (sparkType != null) {
       return sparkType;
     } else if (schema != null) {