Almost all build scripts have target nbm, which builds nbm for given module.
There is needed keystore and storepass defined for it otherwise it fail. Vast
majority of all created nbms will not be signed, so why don't we have property
storepass set to "?" by default in all build scripts. 
Solution is to add following to beginning of each build script:
<property name="storepass" value="?"/>

Production of signed nbms must provide storepass and keystore properties anyway
so it will override default settings.