Deserialize null capabilities in Device entities as empty sets

service/src/main/java/org/whispersystems/textsecuregcm/storage/Device.java

@@ -6,6 +6,7 @@
 
 
 import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonSetter;
 import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
 import com.fasterxml.jackson.databind.annotation.JsonSerialize;
 import java.time.Duration;
@@ -178,6 +179,7 @@ public Set<DeviceCapability> getCapabilities() {
     return capabilities;
   }
 
+  @JsonSetter
   public void setCapabilities(@Nullable final Set<DeviceCapability> capabilities) {
     this.capabilities = (capabilities == null || capabilities.isEmpty())
         ? Collections.emptySet()

service/src/test/java/org/whispersystems/textsecuregcm/storage/DeviceTest.java

@@ -6,11 +6,15 @@
 package org.whispersystems.textsecuregcm.storage;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 
 import java.time.Duration;
 import java.time.Instant;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.CsvSource;
+import org.whispersystems.textsecuregcm.util.SystemMapper;
 
 class DeviceTest {
 
@@ -42,4 +46,25 @@ public void testIsExpired(final boolean primary, final Duration timeSinceLastSee
     assertEquals(expectExpired, device.isExpired());
   }
 
+  @Test
+  void deserializeCapabilities() throws JsonProcessingException {
+    {
+      final Device device = SystemMapper.jsonMapper().readValue("""
+          {
+            "capabilities": null
+          }
+          """, Device.class);
+
+      assertNotNull(device.getCapabilities(),
+          "Device deserialization should populate null capabilities with an empty set");
+    }
+
+    {
+      final Device device = SystemMapper.jsonMapper().readValue("{}", Device.class);
+
+      assertNotNull(device.getCapabilities(),
+          "Device deserialization should populate null capabilities with an empty set");
+    }
+  }
+
 }