code: public static void setGlobalHeader(String name, Object value) {
          if (value != null) {
              globalHeaders.put(name, value);
          } else {
              globalHeaders.remove(name);
          }
      }
docs: Set the value for a named header which is valid for all requests in the running JVM.
  <br>
  The value can be overwritten by calling {@link Webb#setDefaultHeader(String, Object)} and/or
  {@link com.goebl.david.Request#header(String, Object)}.
  <br>
  For the supported types for values see {@link Request#header(String, Object)}.
  
  @param name name of the header (regarding HTTP it is not case-sensitive, but here case is important).
  @param value value of the header. If <code>null</code> the header value is cleared (effectively not set).
  
  @see #setDefaultHeader(String, Object)
  @see com.goebl.david.Request#header(String, Object)