code: public static <K, V> TypeInformation<Map<K, V>> MAP(TypeInformation<K> keyType, TypeInformation<V> valueType) {
  		return new MapTypeInfo<>(keyType, valueType);
  	}
docs: Returns type information for a Java {@link java.util.Map}. A map must not be null. Null values
  in keys are not supported. An entry's value can be null.
  
  <p>By default, maps are untyped and treated as a generic type in Flink; therefore, it is useful
  to pass type information whenever a map is used.
  
  <p><strong>Note:</strong> Flink does not preserve the concrete {@link Map} type. It converts a map into {@link HashMap} when
  copying or deserializing.
  
  @param keyType type information for the map's keys
  @param valueType type information for the map's values