private com.google.protobuf.SingleFieldBuilderV3<
            com.google.protobuf.Duration,
            com.google.protobuf.Duration.Builder,
            com.google.protobuf.DurationOrBuilder>
        getTtlFieldBuilder() {
      if (ttlBuilder_ == null) {
        if (!(expirationCase_ == 10)) {
          expiration_ = com.google.protobuf.Duration.getDefaultInstance();
        }
        ttlBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.protobuf.Duration,
                com.google.protobuf.Duration.Builder,
                com.google.protobuf.DurationOrBuilder>(
                (com.google.protobuf.Duration) expiration_, getParentForChildren(), isClean());
        expiration_ = null;
      }
      expirationCase_ = 10;
      onChanged();
      return ttlBuilder_;
    }
<pre>
Input only. The TTL for this resource. The expiration time is computed:
now + TTL.
</pre>

<code>.google.protobuf.Duration ttl = 10 [(.google.api.field_behavior) = INPUT_ONLY];</code>
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/CachedContent.java