chore: Address PR feedback

Author: lqiu96

google-cloud-bigquery/src/main/java/com/google/cloud/bigquery/BigQueryOptions.java

@@ -230,10 +230,10 @@ public void setThrowNotFound(boolean setThrowNotFound) {
    * Builder#setDataFormatOptions(DataFormatOptions)} to set the int64timestamp configuration
    * instead.
    *
-   * <p>If useInt64Timestamps is set via DataFormatOptions, then that value in DataFormatOptions
-   * will be used.
+   * <p>If useInt64Timestamps is set via DataFormatOptions, then the value in DataFormatOptions will
+   * be used. Otherwise, this value will be passed to DataFormatOptions.
    *
-   * <p>{@code DataFormatOptions.newBuilder().setUseInt64Timestamp(...).build()}
+   * <p>Alternative: {@code DataFormatOptions.newBuilder().setUseInt64Timestamp(...).build()}
    */
   @ObsoleteApi("Use setDataFormatOptions(DataFormatOptions) instead")
   public void setUseInt64Timestamps(boolean useInt64Timestamps) {
@@ -255,6 +255,10 @@ public boolean getThrowNotFound() {
    * This getter is marked as Obsolete. Prefer {@link
    * DataFormatOptions.Builder#useInt64Timestamp(boolean)} to set the int64timestamp configuration
    * instead.
+   *
+   * <p>Warning: DataFormatOptions values have precedence. Use {@link
+   * DataFormatOptions#useInt64Timestamp()} to get `useInt64Timestamp` value used by the BigQuery
+   * client.
    */
   @ObsoleteApi("Use getDataFormatOptions().isUseInt64Timestamp() instead")
   public boolean getUseInt64Timestamps() {

google-cloud-bigquery/src/main/java/com/google/cloud/bigquery/DataFormatOptions.java

@@ -17,7 +17,6 @@
 
 import com.google.auto.value.AutoValue;
 import java.io.Serializable;
-import javax.annotation.Nullable;
 
 /**
  * Google BigQuery DataFormatOptions. Configures the output format for data types returned from
@@ -45,11 +44,12 @@ public String toString() {
 
   public abstract boolean useInt64Timestamp();
 
-  @Nullable
   public abstract TimestampFormatOptions timestampFormatOptions();
 
   public static Builder newBuilder() {
-    return new AutoValue_DataFormatOptions.Builder().useInt64Timestamp(false);
+    return new AutoValue_DataFormatOptions.Builder()
+        .useInt64Timestamp(false)
+        .timestampFormatOptions(TimestampFormatOptions.TIMESTAMP_OUTPUT_FORMAT_UNSPECIFIED);
   }
 
   public abstract Builder toBuilder();
@@ -62,27 +62,19 @@ public abstract static class Builder {
 
     abstract TimestampFormatOptions timestampFormatOptions();
 
-    abstract DataFormatOptions autoBuild();
-
-    public DataFormatOptions build() {
-      if (timestampFormatOptions() == null) {
-        timestampFormatOptions(TimestampFormatOptions.TIMESTAMP_OUTPUT_FORMAT_UNSPECIFIED);
-      }
-      return autoBuild();
-    }
+    public abstract DataFormatOptions build();
   }
 
   com.google.api.services.bigquery.model.DataFormatOptions toPb() {
     com.google.api.services.bigquery.model.DataFormatOptions request =
         new com.google.api.services.bigquery.model.DataFormatOptions();
     request.setUseInt64Timestamp(useInt64Timestamp());
-    if (timestampFormatOptions() != null) {
-      request.setTimestampOutputFormat(timestampFormatOptions().toString());
-    }
+    request.setTimestampOutputFormat(timestampFormatOptions().toString());
     return request;
   }
 
-  DataFormatOptions fromPb(com.google.api.services.bigquery.model.DataFormatOptions request) {
+  static DataFormatOptions fromPb(
+      com.google.api.services.bigquery.model.DataFormatOptions request) {
     AutoValue_DataFormatOptions.Builder builder = new AutoValue_DataFormatOptions.Builder();
     if (request.getUseInt64Timestamp() != null) {
       builder.useInt64Timestamp(request.getUseInt64Timestamp());