public Builder mergeStartTime(com.google.protobuf.Timestamp value) {
          if (startTimeBuilder_ == null) {
            if (((bitField0_ & 0x00000002) != 0)
                && startTime_ != null
                && startTime_ != com.google.protobuf.Timestamp.getDefaultInstance()) {
              getStartTimeBuilder().mergeFrom(value);
            } else {
              startTime_ = value;
            }
          } else {
            startTimeBuilder_.mergeFrom(value);
          }
          if (startTime_ != null) {
            bitField0_ |= 0x00000002;
            onChanged();
          }
          return this;
        }
<pre>
Optional. The starting timestamp for messages to import.
</pre>

<code>
.google.protobuf.Timestamp start_time = 2 [(.google.api.field_behavior) = OPTIONAL];
</code>
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/SlackSource.java