Set a fallback in expand() processing if there is no documentUrl. This uses JsonLdOptions/base, which could be null, or something else appropriate for when the input or expandContext is not a URL.

For #370.

Author: gkellogg

index.html

@@ -5743,7 +5743,7 @@ <h3>Algorithm</h3>
           <li>Initialize a new empty <var>active context</var>.
             The <a>base IRI</a> and <a>original base URL</a> of the <var>active context</var> is set to the {{RemoteDocument/documentUrl}}
             from <var>remote document</var>, if available;
-            otherwise to <code>null</code>.
+            otherwise to {{JsonLdOptions/base}}.
             If set, the {{JsonLdOptions/base}} option from <a data-lt="jsonldprocessor-expand-options">options</a> overrides the <a>base IRI</a>.</li>
           <li>If the {{JsonLdOptions/expandContext}} option in <a data-lt="jsonldprocessor-expand-options">options</a> is set, 
             update the <var>active context</var> using the <a href="#context-processing-algorithm">Context Processing algorithm</a>,
@@ -5759,7 +5759,7 @@ <h3>Algorithm</h3>
             passing the <var>active context</var>,
             {{RemoteDocument/document}} from <var>remote document</var> or <a data-lt="jsonldprocessor-expand-input">input</a>
             if there is no <var>remote document</var> as <var>element</var>,
-            {{RemoteDocument/documentUrl}} as <var>base URL</var>,
+            {{RemoteDocument/documentUrl}} as <var>base URL</var>, if available, otherwise to {{JsonLdOptions/base}},
             and <span class="changed">{{JsonLdOptions/frameExpansion}}</span>
             and <span class="changed">and {{JsonLdOptions/ordered}}</span>
             flags from <a data-lt="jsonldprocessor-compact-options">options</a>.