Resolves a relative
URI object potentially containing a variable reference as its first segment, replacing the variable reference (if any) with the variable's value (which is a concrete absolute URI). If the given URI is absolute or has a non-
null device then no variable substitution is done and that URI is returned as is. If the given URI is relative and has a
null device, but the first segment does not correspond to a defined variable, then the URI is returned as is.
If the given URI is null then null will be returned. In all other cases the result will be non-null.
@param uri the URI to be resolved
@return the resolved URI or
null
@since 3.2