Adding comment about sun classes usage and using a constant for empty byte array

Author: WesleyRosenblum

src/main/java/com/amazonaws/encryptionsdk/internal/Utils.java

@@ -24,6 +24,7 @@
 import java.util.WeakHashMap;
 import java.util.concurrent.atomic.AtomicLong;
 
+import org.apache.commons.lang3.ArrayUtils;
 import org.bouncycastle.util.encoders.Base64;
 
 /**
@@ -268,7 +269,7 @@ public static ByteBuffer limit(final ByteBuffer buff, final int newLimit) {
      * @return decoded data as a byte array
      */
     public static byte[] decodeBase64String(final String encoded) {
-        return encoded.isEmpty() ? new byte[0] : Base64.decode(encoded);
+        return encoded.isEmpty() ? ArrayUtils.EMPTY_BYTE_ARRAY : Base64.decode(encoded);
     }
 
     /**

src/test/java/com/amazonaws/encryptionsdk/jce/KeyStoreProviderTest.java

@@ -43,6 +43,10 @@
 import com.amazonaws.encryptionsdk.MasterKeyProvider;
 import com.amazonaws.encryptionsdk.exception.CannotUnwrapDataKeyException;
 import com.amazonaws.encryptionsdk.multi.MultipleProviderFactory;
+
+/* These internal sun classes are included solely for test purposes as
+   this test cannot use BouncyCastle cert generation, as there are incompatibilities
+   between how standard BC and FIPS BC perform cert generation. */
 import sun.security.x509.AlgorithmId;
 import sun.security.x509.CertificateAlgorithmId;
 import sun.security.x509.CertificateSerialNumber;