Add serializer for BitSet.

src/main/java/li/cil/oc2/serialization/serializers/BitSetSerializer.java

@@ -0,0 +1,36 @@
+package li.cil.oc2.serialization.serializers;
+
+import li.cil.ceres.api.*;
+
+import javax.annotation.Nullable;
+import java.util.BitSet;
+
+@RegisterSerializer
+public final class BitSetSerializer implements Serializer<BitSet> {
+    @Override
+    public void serialize(final SerializationVisitor visitor, final Class<BitSet> type, final Object value) throws SerializationException {
+        visitor.putObject("value", long[].class, ((BitSet) value).toLongArray());
+    }
+
+    @Override
+    public BitSet deserialize(final DeserializationVisitor visitor, final Class<BitSet> type, @Nullable final Object value) throws SerializationException {
+        BitSet bitSet = (BitSet) value;
+        if (!visitor.exists("value")) {
+            return bitSet;
+        }
+
+        final long[] longs = (long[]) visitor.getObject("value", long[].class, null);
+        if (longs == null) {
+            return null;
+        }
+
+        if (bitSet == null) {
+            bitSet = BitSet.valueOf(longs);
+        } else {
+            bitSet.clear();
+            bitSet.or(BitSet.valueOf(longs));
+        }
+
+        return bitSet;
+    }
+}