BigQuery returns NULLABLE mode for a field that has a REQUIRED mode (field created as a NOT NULL from the beginning)

[anneyxa]

Environment details

BigQuery Client Library for Java: google-cloud-bigquery version 2.37.2 and below

I'm using Java 11.

Steps to reproduce

1. Create a table in BigQuery console (or in any other way) with a NOT NULL field, i.e. CREATE TABLE sample.TEST_TABLE ( C1 INT64 NOT NULL, C2 BIGNUMERIC );
2. Use BigQuery Client Library for Java to execute select statement for that table. Received schema should report that C1 column has mode REQUIRED, while it reports the mode as NULLABLE.

Code example

// create a com.google.cloud.bigquery.BigQuery object, i.e.:
// BigQuery bigQuery = BigQueryOptions.newBuilder()......

String query = "SELECT * FROM sample.TEST_TABLE";
Job job = bigQuery.create(JobInfo.of(QueryJobConfiguration.newBuilder(query).build()));
TableResult result = job.getQueryResults();
Schema schema = result.getSchema();

// Print the schema, or print the fields:
List<Field> fields = schema.getFields();
for (Field field : fields) {
    System.out.println("Field Mode: " + field.getMode());
    // C1 column which was created as NOT NULL and has REQUIRED mode in BigQuery console 
    // is being returned here as mode NULLABLE
}

// OR

// create a com.google.cloud.bigquery.BigQuery object, i.e.:
// BigQuery bigQuery = BigQueryOptions.newBuilder()......

String query = "SELECT * FROM sample.TEST_TABLE";
QueryJobConfiguration.Builder configuration = QueryJobConfiguration.newBuilder(query).setDryRun(true);
Schema schema = ((QueryStatistics) bigQuery.create(JobInfo.of(configuration.build())).getStatistics()).getSchema();

System.out.println(schema);
// See at C1 column mode: Should be REQUIRED but is NULLABLE.

Prints out 2 nullable fields.