Merge branch '1011-docker-credentials' into 3.x

Author: twoseat

cloudfoundry-client/src/main/java/org/cloudfoundry/client/v3/packages/_DockerData.java

@@ -18,6 +18,7 @@
 
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
+import org.cloudfoundry.Nullable;
 import org.immutables.value.Value;
 
 /**
@@ -37,12 +38,14 @@ abstract class _DockerData implements PackageData {
      * The password for the image's registry
      */
     @JsonProperty("password")
+    @Nullable
     abstract String getPassword();
 
     /**
      * The username for the image's registry
      */
     @JsonProperty("username")
+    @Nullable
     abstract String getUsername();
 
 }