Test if

#IF parser function

{{#show:Albania/OER| ?Has capital|link=none}} yields Tirana

{{#show:Hungary | ?In OECD}} yields "true"

{{#show:Brazil| ?In OECD}} yields ""

{{#if:string | yes | no}} yields "yes"

{{#if:{{#show:Brazil| ?In OECD}}| yes | no}} yields "no"

{{#if:{{#show:France| ?In OECD}}| yes | no}} yields "yes"

Thus:

{{#if:{{#show:Brazil| ?In OECD}}| [[Category:OECD]]|}} yields ""

{{#if:{{#show:France| ?In OECD}}| [[Category:OECD]]|}} yields ""