<firebase-document 
   path="/settings/termsVersion" 
  data="{{fbTermsVersion}}"></firebase-document>
<!-- termsVersion will be equal to "" when fbTermsVersion is null or {}. Otherwise it is "v0" (primitive, data stored at "settings/termsVersion")-->
<default-value 
  data="{{termsVersion}}"
   input="{{fbTermsVersion}}" 
   default-value=""></default-value>

<firebase-document 
  path="/userData/terms/[[user.uid]]/[[termsVersion]]"  
  data="{{userTerms}}"></firebase-document>
<!-- userTimersSigned is false whenever userTerms id null or {}. Note "object" default-type so that "false" is parsed to false -->
<default-value 
  data="{{userTermsSigned}}" 
  input="{{userTerms}}" 
  default-type="object" 
  default-value="false"></default-value>