correct author/author_handle.json empty strings

Fixed author/author_handle.json situations where "location_code",
"location_name", and/or "deprecated_twitter_handle" was an empty
JSON string.  In those cases the JSON null is used instead.

author/Paul_E_Black.json

@@ -4,12 +4,12 @@
     "author_handle" : "Paul_E_Black",
     "full_name" : "Paul E. Black",
     "sort_word" : "black",
-    "location_code" : "",
-    "location_name" : "",
+    "location_code" : null,
+    "location_name" : null,
     "email" : "p.black@acm.org",
     "url" : "http:\/\/hissa.ncsl.nist.gov\/~black\/black.html",
     "alt_url" : null,
-    "deprecated_twitter_handle" : "",
+    "deprecated_twitter_handle" : null,
     "mastodon" : null,
     "mastodon_url" : null,
     "github" : null,