Mustache engine handles possibly invalid keynames in possibly incorrect way

See https://github.com/mustache/spec/issues/179 for an issue raised on the mustache spec repository.

In brief, mustache.java renders the input data

{ "a.b": "c" }

and template

{{ a.b }}

as

c

which is in a perhaps-incorrect way, although one that is not actually specified by the spec. It is likely that keys are never intended to have periods in them (see https://github.com/mustache/spec/issues/67#issuecomment-53523219), but again, this is not actually specified.

Note that other engines, such as both of the python ones I have checked, render this as a blank.

Note further that the current java engine prioritises a key with a period over nested data: that is, the following data renders probably incorrectly (though again, not actually counter to the specification):

{ "a": { "b": "expected"}, "a.b": "c" }

and

{{ a.b }}

render as

c

which is not what I would expect.

No implementation files or tests are named. Start by reading the linked Mustache specification issue 179, then trace mustache.java's key-resolution behavior for the two examples in this issue. Done means an agreed, specification-backed result for dotted keys and a regression test covering the chosen behavior.