While trying to complete the challenge deployment of a big object through trailhead, workbench repeatedly tells me:



I know what you're going to say. "Jason, just throw a question mark onto the end of the attribute name. That's documented everywhere."
And you're right. Every source I see on Google tells me to simply encapsulate everything with included question marks on both sides. 

But lo, it's already there. Here's my object file:
 

<?xml version="1.0" encoding="UTF-8"?>
<CustomObject xmlns="http://soap.sforce.com/2006/04/metadata">
<deploymentStatus>Deployed</deploymentStatus>
    <fields>
        <fullName>Start_Location_Lat__c</fullName>
        <label>Start Location Latitude</label>       
        <required>false</required>
        <type>Number</type>      
        <scale>4</scale>
        <precision>7</precision>
    </fields>
    <fields>
        <fullName>Start_Location_Long__c</fullName>
        <label>Start Location Longitude</label>       
        <required>false</required>
        <type>Number</type>   
        <scale>4</scale>
        <precision>7</precision>
    </fields>
    <fields>
        <fullName>Start_Time__c</fullName>
        <label>Start Time</label>
        <required>true</required>
        <type>DateTime</type>
        <unique>false</unique>
    </fields>
    <fields>
        <fullName>End_Time__c</fullName>
        <label>End Time</label>
        <required>false</required>
        <type>DateTime</type>
        <unique>false</unique>
    </fields>
    <fields>
        <fullName>Service_Type__c</fullName>
        <label>Service Type</label>
        <length>16</length>
        <required>false</required>
        <type>Text</type>
        <unique>false</unique>
    </fields>
    <fields>
        <fullName>Rider_Account__c</fullName>
        <label>Rider Account</label>
        <length>16</length>
        <required>true</required>
        <type>Text</type>       
    </fields>
    <fields>
        <fullName>Rider_Rating__c</fullName>
        <label>Rider Rating</label>       
        <required>false</required>
        <type>Number</type>
        <unique>false</unique>
        <scale>1</scale>
        <precision>2</precision>
    </fields>
    <indexes>
        <fullName>Rider_History_Index</fullName>
        <label>Rider History Index</label>
        <fields>
            <name>Rider_Account__c</name>
            <sortDirection>DESC</sortDirection>
        </fields>
        <fields>
            <name>Start_Time__c</name>
            <sortDirection>DESC</sortDirection>
        </fields>       
    </indexes>
    <label>Rider History</label>
    <pluralLabel>Rider Histories</pluralLabel>
</CustomObject>