Update schema nullable issue.

Author: JessieYee

database-commons/src/main/java/io/cdap/plugin/db/DBRecord.java

@@ -153,6 +153,7 @@ protected void setField(ResultSet resultSet, StructuredRecord.Builder recordBuil
       recordBuilder.setDecimal(field.getName(), (BigDecimal) o);
     } else if (o instanceof BigInteger) {
       Schema schema = field.getSchema();
+      schema = schema.isNullable() ? schema.getNonNullable() : schema;
       if (schema.getType() == Schema.Type.LONG) {
         recordBuilder.set(field.getName(), ((BigInteger) o).longValueExact());
       } else {