Fix BigQuery NullPointerException when estimatedFields is empty (#3984)

* BigQuery client throws NullPointerException when estimatedFields is empty

* fix formatting

Author: ajaaym

google-cloud-clients/google-cloud-bigquery/src/main/java/com/google/cloud/bigquery/StandardTableDefinition.java

@@ -46,11 +46,11 @@ public abstract class StandardTableDefinition extends TableDefinition {
   public static class StreamingBuffer implements Serializable {
 
     private static final long serialVersionUID = 822027055549277843L;
-    private final long estimatedRows;
-    private final long estimatedBytes;
+    private final Long estimatedRows;
+    private final Long estimatedBytes;
     private final Long oldestEntryTime;
 
-    StreamingBuffer(long estimatedRows, long estimatedBytes, Long oldestEntryTime) {
+    StreamingBuffer(Long estimatedRows, Long estimatedBytes, Long oldestEntryTime) {
       this.estimatedRows = estimatedRows;
       this.estimatedBytes = estimatedBytes;
       this.oldestEntryTime = oldestEntryTime;
@@ -113,8 +113,13 @@ static StreamingBuffer fromPb(Streamingbuffer streamingBufferPb) {
       if (streamingBufferPb.getOldestEntryTime() != null) {
         oldestEntryTime = streamingBufferPb.getOldestEntryTime().longValue();
       }
-      return new StreamingBuffer(streamingBufferPb.getEstimatedRows().longValue(),
-          streamingBufferPb.getEstimatedBytes().longValue(),
+      return new StreamingBuffer(
+          streamingBufferPb.getEstimatedRows() != null
+              ? streamingBufferPb.getEstimatedRows().longValue()
+              : null,
+          streamingBufferPb.getEstimatedBytes() != null
+              ? streamingBufferPb.getEstimatedBytes().longValue()
+              : null,
           oldestEntryTime);
     }
   }

google-cloud-clients/google-cloud-bigquery/src/test/java/com/google/cloud/bigquery/StandardTableDefinitionTest.java

@@ -20,6 +20,7 @@
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 
+import com.google.api.services.bigquery.model.Streamingbuffer;
 import com.google.cloud.bigquery.StandardTableDefinition.StreamingBuffer;
 
 import com.google.common.collect.ImmutableList;
@@ -117,6 +118,12 @@ public void testToAndFromPb() {
         TableDefinition.<StandardTableDefinition>fromPb(definition.toPb()));
   }
 
+  @Test
+  public void testFromPbWithNullEstimatedRowsAndBytes() {
+    StandardTableDefinition.fromPb(
+        TABLE_DEFINITION.toPb().setStreamingBuffer(new Streamingbuffer()));
+  }
+
   private void compareStandardTableDefinition(StandardTableDefinition expected,
       StandardTableDefinition value) {
     assertEquals(expected, value);