Remove Checker Framework; add NullAway, Picnic Error Prone Support.

Change-Id: I6558f0b4db0f9a192c18bbe45e2eaf10595bc666
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Metadata.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Metadata.java
index 6e1f820..62f0331 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Metadata.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Metadata.java
@@ -4,9 +4,10 @@
 
 package eu.mulk.jgvariant.ostree;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
+
 import eu.mulk.jgvariant.core.Decoder;
 import eu.mulk.jgvariant.core.Variant;
-import java.nio.charset.StandardCharsets;
 import java.util.Map;
 
 /**
@@ -19,8 +20,7 @@
 public record Metadata(Map<String, Variant> fields) {
 
   private static final Decoder<Metadata> DECODER =
-      Decoder.ofDictionary(Decoder.ofString(StandardCharsets.UTF_8), Decoder.ofVariant())
-          .map(Metadata::new);
+      Decoder.ofDictionary(Decoder.ofString(UTF_8), Decoder.ofVariant()).map(Metadata::new);
 
   /**
    * Acquires a {@link Decoder} for the enclosing type.