Add empty authorities by default

Closes gh-12533

Author: stillya

core/src/main/java/org/springframework/security/core/userdetails/User.java

@@ -329,7 +329,7 @@ public static final class UserBuilder {
 
 		private String password;
 
-		private List<GrantedAuthority> authorities;
+		private List<GrantedAuthority> authorities = new ArrayList<>();
 
 		private boolean accountExpired;
 
@@ -427,6 +427,7 @@ public UserBuilder roles(String... roles) {
 		 * @see #roles(String...)
 		 */
 		public UserBuilder authorities(GrantedAuthority... authorities) {
+			Assert.notNull(authorities, "authorities cannot be null");
 			return authorities(Arrays.asList(authorities));
 		}
 
@@ -439,7 +440,8 @@ public UserBuilder authorities(GrantedAuthority... authorities) {
 		 * @see #roles(String...)
 		 */
 		public UserBuilder authorities(Collection<? extends GrantedAuthority> authorities) {
-			this.authorities = new ArrayList<>(authorities);
+			Assert.notNull(authorities, "authorities cannot be null");
+			this.authorities.addAll(authorities);
 			return this;
 		}
 
@@ -452,6 +454,7 @@ public UserBuilder authorities(Collection<? extends GrantedAuthority> authoritie
 		 * @see #roles(String...)
 		 */
 		public UserBuilder authorities(String... authorities) {
+			Assert.notNull(authorities, "authorities cannot be null");
 			return authorities(AuthorityUtils.createAuthorityList(authorities));
 		}
 

core/src/test/java/org/springframework/security/core/userdetails/UserTests.java

@@ -18,6 +18,8 @@
 
 import java.io.ByteArrayOutputStream;
 import java.io.ObjectOutputStream;
+import java.util.ArrayList;
+import java.util.Collection;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
@@ -37,6 +39,7 @@
  * Tests {@link User}.
  *
  * @author Ben Alex
+ * @author Ilya Starchenko
  */
 public class UserTests {
 
@@ -68,6 +71,33 @@ public void testNoArgConstructorDoesntExist() {
 				.isThrownBy(() -> User.class.getDeclaredConstructor((Class[]) null));
 	}
 
+	@Test
+	public void testBuildUserWithNoAuthorities() {
+		UserDetails user = User.builder().username("user").password("password").build();
+		assertThat(user.getAuthorities()).isEmpty();
+	}
+
+	@Test
+	public void testNullWithinUserAuthoritiesIsRejected() {
+		assertThatIllegalArgumentException().isThrownBy(() -> User.builder().username("user").password("password")
+				.authorities((Collection<? extends GrantedAuthority>) null).build());
+		List<GrantedAuthority> authorities = new ArrayList<>();
+		authorities.add(null);
+		authorities.add(null);
+		assertThatIllegalArgumentException().isThrownBy(
+				() -> User.builder().username("user").password("password").authorities(authorities).build());
+
+		assertThatIllegalArgumentException().isThrownBy(() -> User.builder().username("user").password("password")
+				.authorities((GrantedAuthority[]) null).build());
+		assertThatIllegalArgumentException().isThrownBy(() -> User.builder().username("user").password("password")
+				.authorities(new GrantedAuthority[] { null, null }).build());
+
+		assertThatIllegalArgumentException().isThrownBy(
+				() -> User.builder().username("user").password("password").authorities((String[]) null).build());
+		assertThatIllegalArgumentException().isThrownBy(() -> User.builder().username("user").password("password")
+				.authorities(new String[] { null, null }).build());
+	}
+
 	@Test
 	public void testNullValuesRejected() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new User(null, "koala", true, true, true, true, ROLE_12));