Polish PemSslBundleProperties

See gh-36281

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/ssl/PemSslBundleProperties.java

@@ -31,12 +31,12 @@ public class PemSslBundleProperties extends SslBundleProperties {
 	/**
 	 * Keystore properties.
 	 */
-	private Store keystore = new Store();
+	private final Store keystore = new Store();
 
 	/**
 	 * Truststore properties.
 	 */
-	private Store truststore = new Store();
+	private final Store truststore = new Store();
 
 	public Store getKeystore() {
 		return this.keystore;
@@ -54,22 +54,22 @@ public class PemSslBundleProperties extends SslBundleProperties {
 		/**
 		 * Type of the store to create, e.g. JKS.
 		 */
-		String type;
+		private String type;
 
 		/**
 		 * Location or content of the certificate in PEM format.
 		 */
-		String certificate;
+		private String certificate;
 
 		/**
 		 * Location or content of the private key in PEM format.
 		 */
-		String privateKey;
+		private String privateKey;
 
 		/**
 		 * Password used to decrypt an encrypted private key.
 		 */
-		String privateKeyPassword;
+		private String privateKeyPassword;
 
 		public String getType() {
 			return this.type;