code: @SuppressWarnings("unchecked")
    public boolean getBooleanValue() {
      String stringValue = getStringValue();
      checkState(
          stringValue.equalsIgnoreCase("true") || stringValue.equalsIgnoreCase("false"),
          "Field value is not of boolean type");
      return Boolean.parseBoolean(stringValue);
    }
docs: Returns this field's value as a {@link Boolean}. This method should only be used if the
  corresponding field has {@link LegacySQLTypeName#BOOLEAN} type.
  
  @throws ClassCastException if the field is not a primitive type
  @throws IllegalStateException if the field's value could not be converted to {@link Boolean}
  @throws NullPointerException if {@link #isNull()} returns {@code true}