[Bug]: BigQueryIO got JSON parsing error: No such field when there is no field, or field is empty string

### What happened?

I tried searching for previous reports and didn't find anything.

Currently writing custom Dataflow templates to write to BigQuery using Java SDK.

```
2.45.0
v2-rev20200719-1.30.10
1.30.10
1.34.0
```

I am trying to run pipeline with `BigQueryIO.writeTableRows()` with schema specified, but mode not specified so it should be `NULLABLE`

However, if `TableRow` from previous stage does not contain field, it gives error:
```
Error while reading data, error message: JSON parsing error in row starting at position 16645: No such field: user_address.
```
In temp file, the relevant object does not have the field shown in error.

In another instance, `TableRow` from previous stage contains the field, but the field is an empty string. It gives error:
```
Error while reading data, error message: JSON parsing error in row starting at position 0: No such field: user_address.
```

### Issue Priority

Priority: 2 (default / most bugs should be filed as P2)

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