@SuppressWarnings("varargs")
    @SafeVarargs
    public static <T> ToString<T> joining(
            CharSequence separator,
            ToString<T>... expressions) {
        return joining(separator, "", "", expressions);
    }
Returns an expression that represents the result of all the specified
expressions joined together with separators between them, forming a
single string.

@param separator    the separator (may be empty but never {@code null})
@param expressions  the array of expressions to join
@param <T>          the input entity type
@return             the joined expression
runtime-parent/runtime-compute/src/main/java/com/speedment/runtime/compute/expression/Expressions.java