Issue #2941323 by quietone, joachim: StaticMap should document how/whether it...

 *       'TRUE': to

 * @endcode

 *

 * A NULL can be mapped. If the value of the source property 'foo' is NULL then

 * the value of the destination property bar will be 'to'.

 *

 * @code

 * process:

 *   bar:

 *     plugin: static_map

 *     source: foo

 *     map:

 *       NULL: to

 * @endcode

 *

 * If your source data contains booleans, the boolean is treated as a numeric 0

 * or 1. If the value of the source property 'foo' is TRUE then the value of the

 * destination property bar will be 'bar'. And if the value of the source

 * property 'foo' is FALSE then the value of the destination property bar will

 * be 'bar'.

 *

 * @code

 * process:

 *   bar:

 *     plugin: static_map

 *     source: foo

 *     map:

 *       0: foo

 *       1: bar

 * @endcode

 *

 * Mapping from a string which contains a period is not supported. A custom

 * process plugin can be written to handle this kind of a transformation.

 * Another option which may be feasible in certain use cases is to first pass