Don't allow a list of the empty string in List<String> fields (#2011)

If the user does, e.g. `--allowed_nameservers=` (or contact ids) that
shouldn't mean a list consisting solely of the empty string.

Using this parameter / converter allows us to ensure that lists of
strings look reasonable.

core/src/test/java/google/registry/tools/CreateRegistrarCommandTest.java

@@ -321,28 +321,6 @@ class CreateRegistrarCommandTest extends CommandTestCase<CreateRegistrarCommand>
         .inOrder();
   }
 
-  @Test
-  void testSuccess_ipAllowListFlagNull() throws Exception {
-    runCommandForced(
-        "--name=blobio",
-        "--password=some_password",
-        "--registrar_type=REAL",
-        "--iana_id=8",
-        "--ip_allow_list=null",
-        "--passcode=01234",
-        "--icann_referral_email=foo@bar.test",
-        "--street=\"123 Fake St\"",
-        "--city Fakington",
-        "--state MA",
-        "--zip 00351",
-        "--cc US",
-        "clientz");
-
-    Optional<Registrar> registrar = Registrar.loadByRegistrarId("clientz");
-    assertThat(registrar).isPresent();
-    assertThat(registrar.get().getIpAddressAllowList()).isEmpty();
-  }
-
   @Test
   void testSuccess_clientCertFileFlag() throws Exception {
     fakeClock.setTo(DateTime.parse("2020-11-01T00:00:00Z"));

core/src/test/java/google/registry/tools/CreateTldCommandTest.java

@@ -451,6 +451,16 @@ class CreateTldCommandTest extends CommandTestCase<CreateTldCommand> {
         .containsExactly("alice", "bob");
   }
 
+  @Test
+  void testSuccess_emptyAllowedRegistrants() throws Exception {
+    runCommandForced(
+        "--allowed_registrants=",
+        "--roid_suffix=Q9JYB4C",
+        "--dns_writers=VoidDnsWriter",
+        "xn--q9jyb4c");
+    assertThat(Tld.get("xn--q9jyb4c").getAllowedRegistrantContactIds()).isEmpty();
+  }
+
   @Test
   void testSuccess_setAllowedNameservers() throws Exception {
     runCommandForced(
@@ -462,6 +472,16 @@ class CreateTldCommandTest extends CommandTestCase<CreateTldCommand> {
         .containsExactly("ns1.example.com", "ns2.example.com");
   }
 
+  @Test
+  void testSuccess_emptyAllowedNameservers() throws Exception {
+    runCommandForced(
+        "--allowed_nameservers=",
+        "--roid_suffix=Q9JYB4C",
+        "--dns_writers=FooDnsWriter",
+        "xn--q9jyb4c");
+    assertThat(Tld.get("xn--q9jyb4c").getAllowedFullyQualifiedHostNames()).isEmpty();
+  }
+
   @Test
   void testSuccess_setCommonReservedListOnTld() throws Exception {
     runSuccessfulReservedListsTest("common_abuse");

core/src/test/java/google/registry/tools/UpdateRegistrarCommandTest.java

@@ -207,21 +207,6 @@ class UpdateRegistrarCommandTest extends CommandTestCase<UpdateRegistrarCommand>
         .inOrder();
   }
 
-  @Test
-  void testSuccess_clearIpAllowList_useNull() throws Exception {
-    persistResource(
-        loadRegistrar("NewRegistrar")
-            .asBuilder()
-            .setIpAddressAllowList(
-                ImmutableList.of(
-                    CidrAddressBlock.create("192.168.1.1"),
-                    CidrAddressBlock.create("192.168.0.2/16")))
-            .build());
-    assertThat(loadRegistrar("NewRegistrar").getIpAddressAllowList()).isNotEmpty();
-    runCommand("--ip_allow_list=null", "--force", "NewRegistrar");
-    assertThat(loadRegistrar("NewRegistrar").getIpAddressAllowList()).isEmpty();
-  }
-
   @Test
   void testSuccess_clearIpAllowList_useEmpty() throws Exception {
     persistResource(

core/src/test/java/google/registry/tools/UpdateTldCommandTest.java

@@ -429,6 +429,17 @@ class UpdateTldCommandTest extends CommandTestCase<UpdateTldCommand> {
         .containsExactly("alice", "bob");
   }
 
+  @Test
+  void testSuccess_emptyAllowedRegistrants() throws Exception {
+    persistResource(
+        Tld.get("xn--q9jyb4c")
+            .asBuilder()
+            .setAllowedRegistrantContactIds(ImmutableSet.of("jane", "john"))
+            .build());
+    runCommandForced("--allowed_registrants=", "xn--q9jyb4c");
+    assertThat(Tld.get("xn--q9jyb4c").getAllowedRegistrantContactIds()).isEmpty();
+  }
+
   @Test
   void testSuccess_addAllowedRegistrants() throws Exception {
     persistResource(
@@ -483,6 +494,17 @@ class UpdateTldCommandTest extends CommandTestCase<UpdateTldCommand> {
         .containsExactly("ns1.example.com", "ns2.example.com");
   }
 
+  @Test
+  void testSuccess_emptyAllowedNameservers() throws Exception {
+    persistResource(
+        Tld.get("xn--q9jyb4c")
+            .asBuilder()
+            .setAllowedFullyQualifiedHostNames(ImmutableSet.of("ns1.example.com"))
+            .build());
+    runCommandForced("--allowed_nameservers=", "xn--q9jyb4c");
+    assertThat(Tld.get("xn--q9jyb4c").getAllowedFullyQualifiedHostNames()).isEmpty();
+  }
+
   @Test
   void testSuccess_addAllowedNameservers() throws Exception {
     persistResource(

core/src/test/java/google/registry/tools/params/StringListParameterTest.java

@@ -0,0 +1,45 @@
+// Copyright 2023 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.tools.params;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+/** Tests for {@link StringListParameter}. */
+public class StringListParameterTest {
+
+  private final StringListParameter instance = new StringListParameter();
+
+  @Test
+  void testSingleItem() {
+    assertThat(instance.convert("foo")).containsExactly("foo");
+  }
+
+  @Test
+  void testMultipleItems() {
+    assertThat(instance.convert("foo,bar")).containsExactly("foo", "bar");
+  }
+
+  @Test
+  void testOmitsEmpty() {
+    assertThat(instance.convert("foo,,bar")).containsExactly("foo", "bar");
+  }
+
+  @Test
+  void testEntirelyEmpty() {
+    assertThat(instance.convert("")).isEmpty();
+  }
+}