fix: Fix some issues with StringUtilBenchmark

* Make `Random` static even though in practice it should only be
  created once already (fixes SpotBugs warning)
* Initialize fields to empty to prevent warning "`@NullMarked` fields
  must be initialized"
* Iterate over `decodedData` directly instead of using the `DATA_COUNT`
  constant even though in practice these should always have the same
  length
* Fill data fields directly instead of using a local
  variables/parameters with the same names

Author: dwalluck

src/test/java/com/github/packageurl/internal/StringUtilBenchmark.java

@@ -54,17 +54,21 @@
 @OutputTimeUnit(TimeUnit.MICROSECONDS)
 @State(Scope.Benchmark)
 public class StringUtilBenchmark {
+    private static final Random RANDOM = new Random();
 
     private static final int DATA_COUNT = 1000;
+
     private static final int DECODED_LENGTH = 256;
+
     private static final byte[] UNRESERVED =
             "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~".getBytes(StandardCharsets.US_ASCII);
 
     @Param({"0", "0.1", "0.5"})
     private double nonAsciiProb;
 
-    private String[] decodedData;
-    private String[] encodedData;
+    private String[] decodedData = {};
+
+    private String[] encodedData = {};
 
     @Setup
     public void setup() {
@@ -73,15 +77,14 @@ public void setup() {
     }
 
     private String[] createDecodedData() {
-        Random random = new Random();
-        String[] decodedData = new String[DATA_COUNT];
+        decodedData = new String[DATA_COUNT];
         for (int i = 0; i < DATA_COUNT; i++) {
             char[] chars = new char[DECODED_LENGTH];
             for (int j = 0; j < DECODED_LENGTH; j++) {
-                if (random.nextDouble() < nonAsciiProb) {
-                    chars[j] = (char) (Byte.MAX_VALUE + 1 + random.nextInt(Short.MAX_VALUE - Byte.MAX_VALUE - 1));
+                if (RANDOM.nextDouble() < nonAsciiProb) {
+                    chars[j] = (char) (Byte.MAX_VALUE + 1 + RANDOM.nextInt(Short.MAX_VALUE - Byte.MAX_VALUE - 1));
                 } else {
-                    chars[j] = (char) UNRESERVED[random.nextInt(UNRESERVED.length)];
+                    chars[j] = (char) UNRESERVED[RANDOM.nextInt(UNRESERVED.length)];
                 }
             }
             decodedData[i] = new String(chars);
@@ -105,8 +108,8 @@ private static String[] encodeData(String[] decodedData) {
 
     @Benchmark
     public void baseline(Blackhole blackhole) {
-        for (int i = 0; i < DATA_COUNT; i++) {
-            byte[] buffer = decodedData[i].getBytes(StandardCharsets.UTF_8);
+        for (String decodedStr : decodedData) {
+            byte[] buffer = decodedStr.getBytes(StandardCharsets.UTF_8);
             // Prevent JIT compiler from assuming the buffer was not modified
             for (int idx = 0; idx < buffer.length; idx++) {
                 buffer[idx] ^= 0x20;