Compilation error on templateTex: files included on thesis.lyx must have at least one definition environment

[htadashi]

First of all, thanks to @lfigueredo for this beautiful template! 💯
I found the following bug on thesis.lyx: if the files included on thesis.lyx does not contain a definition environment, the compilation (tested on LyX 2.2.2) returns the following errors:

! LaTeX Error: Environment defn undefined.

See the LaTeX manual or LaTeX Companion for explanation.
Type H for immediate help.
...

l.183 \renewenvironment{defn}
{%\stepcounter{defn}%
Try typing to proceed.
If that doesn't work, type X to quit.

The same happens with the Theorem and Lemma environments.