fix a case on some shells that the declare results on a undeclared variable

[jhonatanTeixeira]

leading to an assertion error

Just added equal signs to the declare, so it behave correctly, and the if -z assertion works as intended. However, i only tested on ubuntu 18 machine, wich is the OS that was trying to use this script.

[sonatypecla]

Thanks for the contribution! Before we can merge this, we need @jhonatanTeixeira to sign the Sonatype Contributor License Agreement.

[tuxBurner]

Could we please merge this ?

I wasted another hour to find the same solution :)

[Guararapes]

I have just signed the contributor licence