https://tools.ietf.org/html/rfc7230#section-3.2 allows empty field values.

     header-field   = field-name ":" OWS field-value OWS

     field-name     = token
     field-value    = *( field-content / obs-fold )
     field-content  = field-vchar [ 1*( SP / HTAB ) field-vchar ]
     field-vchar    = VCHAR / obs-text

A recipient MAY combine multiple header fields with the same name into one.

   A recipient MAY combine multiple header fields with the same field
   name into one "field-name: field-value" pair, without changing the
   semantics of the message, by appending each subsequent field value to
   the combined field value in order, separated by a comma.  The order
   in which header fields with the same field name are received is
   therefore significant to the interpretation of the combined field
   value; a proxy MUST NOT change the order of these field values when
   forwarding a message.

Hence, if we have response headers r such as

 name:
 name: abc

, r->GetNormalizedHeaders("x", &value) should return true and |value|
should be ", abc". Now it returns true but |value| is "abc".