Fix: boolean values support in non-prepared query

[vgreb]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Licence	Apache-2.0
Fixed tickets

[xavierleune]

Thanks for your PR, I can see some improvements:

• use a case "NULL" (cf gettype(null)) with the same output than integer and double, as we should not output the string 'null' like you did
• improve the unit test by checking the generated output, not only that the real_escape_string has not been called

what do you think ?

[vgreb]

Hi,

I had to explicitly return 'null' otherwise the tests do not pass (cf. previous runs https://github.com/ccmbenchmark/ting/actions/runs/2147218060).

I will improve tests to verify generated output.

[vgreb]

After further investigation, here the explication why we need to return 'null':

call to preg_replace_callback will cast null into a empty string (cf. example)