code: public static void notEmpty(@Nullable final Map<?, ?> map,
        final Supplier<String> messageSupplier) {
      if (CollectionUtils.isEmpty(map)) {
        throw new IllegalArgumentException(Assert.nullSafeGet(messageSupplier));
      }
    }
docs: Assert that a Map contains entries; that is, it must not be {@code null} and must contain at
  least one entry.
  
  <pre class="code">
  Assert.notEmpty(map, () -&gt; "The " + mapType + " map must contain entries");
  </pre>
  
  @param map the map to check
  @param messageSupplier a supplier for the exception message to use if the assertion fails
  @throws IllegalArgumentException if the map is {@code null} or contains no entries
  @since 5.0