title: R to BigQuery Data Upload Error
body: <p>I'm using the R package "bigrquery" to upload data from an R data frame into an existing BigQuery table as follows:</p>
  
  <pre><code>mybq = bq_table(project='...', dataset='...', table=...)
  bq_table_upload(x=mybq, values=..., create_disposition='CREATE_NEVER', 
                  write_disposition='WRITE_APPEND')
  </code></pre>
  
  <p>But I'm the following error message:</p>
  
  <blockquote>
    <p>Error: Invalid schema update. Field NewID has changed type from STRING to INTEGER</p>
  </blockquote>
  
  <p>BigQuery appears to be auto-detecting the data format and mistakenly thinks the NewID column, which has values like "00487", is numeric when it's actually a string. When I append an "x" character to the NewID values, then the error goes away and the upload functions perfectly. Is there any way to disable the auto-detection when uploading data using the "bigrquery" package?</p>