diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/ByteString.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/ByteString.java
index 3a8185c..cfe3635 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/ByteString.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/ByteString.java
@@ -10,6 +10,7 @@
 import java.util.HexFormat;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * A wrapper for a {@code byte[]} that implements {@link #equals(Object)}, {@link #hashCode()}, and
@@ -31,7 +32,7 @@
   }
 
   @Override
-  public boolean equals(Object o) {
+  public boolean equals(@Nullable Object o) {
     return (o instanceof ByteString byteString) && Arrays.equals(bytes, byteString.bytes);
   }
 
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaSuperblock.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaSuperblock.java
index 52b970f..50da203 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaSuperblock.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaSuperblock.java
@@ -70,20 +70,20 @@
               Decoder.ofByteArray().map(DeltaSuperblock::parseDeltaNameList),
               Decoder.ofArray(DeltaMetaEntry.decoder()).withByteOrder(ByteOrder.LITTLE_ENDIAN),
               Decoder.ofArray(DeltaFallback.decoder()).withByteOrder(ByteOrder.LITTLE_ENDIAN))
-          .map(
-              deltaSuperblock -> {
-                // Fix up the endianness of the 'entries' and 'fallbacks' fields, which have
-                // unspecified byte order.
-                var endiannessMetadatum =
-                    deltaSuperblock.metadata().fields().get("ostree.endianness");
-                if (endiannessMetadatum != null
-                    && endiannessMetadatum.value() instanceof Byte endiannessByte
-                    && endiannessByte == (byte) 'B') {
-                  return deltaSuperblock.byteSwapped();
-                } else {
-                  return deltaSuperblock;
-                }
-              });
+          .map(DeltaSuperblock::byteSwappedIfBigEndian);
+
+  private DeltaSuperblock byteSwappedIfBigEndian() {
+    // Fix up the endianness of the 'entries' and 'fallbacks' fields, which have
+    // unspecified byte order.
+    var endiannessMetadatum = metadata().fields().get("ostree.endianness");
+    if (endiannessMetadatum != null
+        && endiannessMetadatum.value() instanceof Byte endiannessByte
+        && endiannessByte == (byte) 'B') {
+      return byteSwapped();
+    } else {
+      return this;
+    }
+  }
 
   private DeltaSuperblock byteSwapped() {
     return new DeltaSuperblock(