sdks:java:io:google-cloud-platform:javadoc generating "cannot find symbol" warnings

> Task :sdks:java:io:google-cloud-platform:javadoc
/usr/local/google/home/suztomo/beam6/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/spanner/SpannerIO.java:912: error: cannot find symbol
      extends PTransform<PCollection<MutationGroup>, SpannerWriteResult> {
              ^
  symbol:   class PTransform
  location: class SpannerIO
/usr/local/google/home/suztomo/beam6/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/spanner/SpannerIO.java:912: error: cannot find symbol
      extends PTransform<PCollection<MutationGroup>, SpannerWriteResult> {
                         ^
  symbol:   class PCollection
  location: class SpannerIO
/usr/local/google/home/suztomo/beam6/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/BigQueryIO.java:700: error: cannot find symbol
  public abstract static class TypedRead<T> extends PTransform<PBegin, PCollection<T>> {
                                                    ^
  symbol:   class PTransform
  location: class BigQueryIO
/usr/local/google/home/suztomo/beam6/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/BigQueryIO.java:700: error: cannot find symbol
  public abstract static class TypedRead<T> extends PTransform<PBegin, PCollection<T>> {
                                                               ^
  symbol:   class PBegin
  location: class BigQueryIO
/usr/local/google/home/suztomo/beam6/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/BigQueryIO.java:700: error: cannot find symbol
  public abstract static class TypedRead<T> extends PTransform<PBegin, PCollection<T>> {
                                                                       ^
  symbol:   class PCollection
  location: class BigQueryIO
/usr/local/google/home/suztomo/beam6/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/BigQueryIO.java:452: warning - Tag @link: can't find withQueryPriority(
 TypedRead.QueryPriority) in org.apache.beam.sdk.io.gcp.bigquery.BigQueryIO.TypedRead
/usr/local/google/home/suztomo/beam6/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/testing/FakeBigQueryServices.java:80: warning - Tag @link: can't find FakeBigQueryServerStream in org.apache.beam.sdk.io.gcp.testing.FakeBigQueryServices.FakeBigQueryServerStream
7 warnings