Core: Fix NPE caused by Unboxing a Null in ManifestFileUtil (apache#2492

) (apache#2495)

* Core: Fix NPE caused by Unboxing a Null in ManifestFileUtil

Previously the boxed value of containsNaN would be null if the table
was made before NaN stats were implemented. This leads to an NPE when
being unboxed. To fix this on null we report "true" since we do not know if the
 partition contains any NaN values.

core/src/main/java/org/apache/iceberg/util/ManifestFileUtil.java

@@ -51,7 +51,7 @@ private static class FieldSummary<T> {
       this.lowerBound = Conversions.fromByteBuffer(primitive, summary.lowerBound());
       this.upperBound = Conversions.fromByteBuffer(primitive, summary.upperBound());
       this.containsNull = summary.containsNull();
-      this.containsNaN = summary.containsNaN();
+      this.containsNaN = summary.containsNaN() == null ? true : summary.containsNaN();
     }
 
     boolean canContain(Object value) {