Treat blank strings as null identity keys

service/src/main/java/org/whispersystems/textsecuregcm/util/IdentityKeyAdapter.java

@@ -49,6 +49,10 @@ public class IdentityKeyAdapter {
         throw new JsonParseException(parser, "Could not parse identity key as a base64-encoded value", e);
       }
 
+      if (identityKeyBytes.length == 0) {
+        return null;
+      }
+
       try {
         return new IdentityKey(identityKeyBytes);
       } catch (final InvalidKeyException e) {

service/src/test/java/org/whispersystems/textsecuregcm/util/IdentityKeyAdapterTest.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2023 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.util;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
+import com.fasterxml.jackson.databind.annotation.JsonSerialize;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.signal.libsignal.protocol.IdentityKey;
+import org.signal.libsignal.protocol.ecc.Curve;
+
+import javax.annotation.Nullable;
+
+import java.util.Base64;
+import java.util.stream.Stream;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class IdentityKeyAdapterTest {
+
+  private static final IdentityKey IDENTITY_KEY = new IdentityKey(Curve.generateKeyPair().getPublicKey());
+
+  private record IdentityKeyCarrier(@JsonSerialize(using = IdentityKeyAdapter.Serializer.class)
+                                    @JsonDeserialize(using = IdentityKeyAdapter.Deserializer.class)
+                                    IdentityKey identityKey) {
+
+  };
+
+  @ParameterizedTest
+  @MethodSource
+  void deserialize(final String json, @Nullable final IdentityKey expectedIdentityKey) throws JsonProcessingException {
+    final IdentityKeyCarrier identityKeyCarrier = SystemMapper.jsonMapper().readValue(json, IdentityKeyCarrier.class);
+
+    assertEquals(expectedIdentityKey, identityKeyCarrier.identityKey());
+  }
+
+  private static Stream<Arguments> deserialize() {
+    final String template = """
+        {
+          "identityKey": %s
+        }
+        """;
+
+    return Stream.of(
+        Arguments.of(String.format(template, "null"), null),
+        Arguments.of(String.format(template, "\"\""), null),
+        Arguments.of(String.format(template, "\"" + Base64.getEncoder().encodeToString(IDENTITY_KEY.serialize()) + "\""), IDENTITY_KEY)
+    );
+  }
+}