feat: Add getStringOrDefault method to FieldValue (#3255)

* feat: Add getStringOrDefault method to FieldValue

* feat: Add getStringOrDefault method to FieldValue

* Add null case to FieldValueTest unit test

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

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

@@ -123,6 +123,20 @@ public String getStringValue() {
     return (String) value;
   }
 
+  /**
+   * Returns this field's value as a {@link String}, or defaultValue if {@link #isNull()} returns
+   * {@code true}. See {@link #getStringValue()} for more details.
+   *
+   * @throws ClassCastException if the field is not a primitive type
+   */
+  @SuppressWarnings("unchecked")
+  public String getStringValueOrDefault(String defaultValue) {
+    if (isNull()) {
+      return defaultValue;
+    }
+    return getStringValue();
+  }
+
   /**
    * Returns this field's value as a byte array. This method should only be used if the
    * corresponding field has primitive type ({@link LegacySQLTypeName#BYTES}.

google-cloud-bigquery/src/test/java/com/google/cloud/bigquery/FieldValueTest.java

@@ -20,6 +20,7 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
 
 import com.google.api.client.util.Data;
 import com.google.api.services.bigquery.model.TableCell;
@@ -77,12 +78,14 @@ public void testFromPb() {
     value = FieldValue.fromPb(GEOGRAPHY_FIELD);
     assertEquals(FieldValue.Attribute.PRIMITIVE, value.getAttribute());
     assertEquals("POINT(-122.350220 47.649154)", value.getStringValue());
+    assertEquals("POINT(-122.350220 47.649154)", value.getStringValueOrDefault(null));
     value = FieldValue.fromPb(NUMERIC_FIELD);
     assertEquals(FieldValue.Attribute.PRIMITIVE, value.getAttribute());
     assertEquals(new BigDecimal("123456789.123456789"), value.getNumericValue());
     value = FieldValue.fromPb(STRING_FIELD);
     assertEquals(FieldValue.Attribute.PRIMITIVE, value.getAttribute());
     assertEquals("string", value.getStringValue());
+    assertEquals("string", value.getStringValueOrDefault(null));
     value = FieldValue.fromPb(TIMESTAMP_FIELD);
     assertEquals(FieldValue.Attribute.PRIMITIVE, value.getAttribute());
     assertEquals(42000000, value.getTimestampValue());
@@ -92,11 +95,13 @@ public void testFromPb() {
         PeriodDuration.of(Period.of(3, 2, 1), Duration.parse("PT12H34M56.789S"));
     assertEquals(periodDuration, value.getPeriodDuration());
     assertEquals("P3Y2M1DT12H34M56.789S", value.getStringValue());
+    assertEquals("P3Y2M1DT12H34M56.789S", value.getStringValueOrDefault(null));
     value = FieldValue.fromPb(INTERVAL_FIELD_2);
     assertEquals(FieldValue.Attribute.PRIMITIVE, value.getAttribute());
     periodDuration = PeriodDuration.of(Period.of(3, 2, 1), Duration.parse("PT12H34M56.789S"));
     assertEquals(periodDuration, value.getPeriodDuration());
     assertEquals("3-2 1 12:34:56.789", value.getStringValue());
+    assertEquals("3-2 1 12:34:56.789", value.getStringValueOrDefault(null));
     value = FieldValue.fromPb(BYTES_FIELD);
     assertEquals(FieldValue.Attribute.PRIMITIVE, value.getAttribute());
     assertArrayEquals(BYTES, value.getBytesValue());
@@ -113,6 +118,10 @@ public void testFromPb() {
     assertEquals(FieldValue.Attribute.RECORD, value.getAttribute());
     assertEquals(FieldValue.fromPb(FLOAT_FIELD), value.getRepeatedValue().get(0));
     assertEquals(FieldValue.fromPb(TIMESTAMP_FIELD), value.getRepeatedValue().get(1));
+    value = FieldValue.fromPb(NULL_FIELD);
+    assertTrue(value.isNull());
+    assertEquals(null, value.getStringValueOrDefault(null));
+    assertEquals("defaultValue", value.getStringValueOrDefault("defaultValue"));
   }
 
   @Test