Add '@any' to inverse context, and set as type/language value for an empty list so that a list term will be selected for an empty list.

See json-ld/json-ld.org#508.

Author: gkellogg

example-files/pr-509.jsonld

@@ -0,0 +1,10 @@
+{
+  "@context": {
+    "name": {
+      "@type": "@id",
+      "@container": "@list",
+      "@id": "https://schema.org/name"
+    }
+  },
+  "name": []
+}

lib/json/ld/context.rb

@@ -1052,7 +1052,7 @@ def compact_iri(iri, value: nil, vocab: nil, reverse: false, quiet: false, **opt
 
       if vocab && inverse_context.has_key?(iri)
         #log_debug("") {"vocab and key in inverse context"} unless quiet
-        default_language = self.default_language || @none
+        default_language = self.default_language || "@none"
         containers = []
         tl, tl_value = "@language", "@null"
 
@@ -1136,7 +1136,8 @@ def compact_iri(iri, value: nil, vocab: nil, reverse: false, quiet: false, **opt
             preferred_values.concat(%w(@id @vocab @none))
           end
         else
-          preferred_values.concat([tl_value, '@none'])
+          tl = '@any' if list?(value) && value['@list'].empty?
+          preferred_values.concat([tl_value, '@none'].compact)
         end
         #log_debug("") {"preferred_values: #{preferred_values.inspect}"} unless quiet
         if p_term = select_term(iri, containers, tl, preferred_values)
@@ -1483,9 +1484,11 @@ def inverse_context
           next unless td = term_definitions[term]
           container = td.container_mapping || (td.as_set ? '@set' : '@none')
           container_map = result[td.id.to_s] ||= {}
-          tl_map = container_map[container] ||= {'@language' => {}, '@type' => {}}
+          tl_map = container_map[container] ||= {'@language' => {}, '@type' => {}, '@any' => {}}
           type_map = tl_map['@type']
           language_map = tl_map['@language']
+          any_map = tl_map['@any']
+          any_map['@none'] ||= term
           if td.reverse_property
             type_map['@reverse'] ||= term
           elsif td.type_mapping

lib/json/ld/frame.rb

@@ -224,7 +224,6 @@ def cleanup_preserve(input, bnodes_to_clear)
         output = Hash.new
         input.each do |key, value|
           if key == '@preserve'
-            #require 'byebug'; byebug
             # replace all key-value pairs where the key is @preserve with the value from the key-pair
             output = cleanup_preserve(value, bnodes_to_clear)
           elsif context.expand_iri(key) == '@id' && bnodes_to_clear.include?(value)