blah.txt

### 1. Steps to reproduce and a small code sample that demonstrates the issue
<!--
// Example: a code sample which creates a document in the local document store.

DocumentStore documentStore;
// ...
DocumentRevision doc = new DocumentRevision();
doc.setBody(DocumentBodyFactory.create("{\"_foo\":\"bar\"}".getBytes()));
documentStore.database().create(doc);
-->

### 2. What you expected to happen
<!--
Example:

I expected the document to be saved to the local document store.
-->

### 3.
<!--
Example:

The following exception was thrown:
"com.cloudant.sync.documentstore.InvalidDocumentException: Field name start with '_' is not allowed."
-->