Add support for empty strinngs in SetInputArrayToProcess.

SetInputArrayToProcess ignored empty strings (treating them same as NULL
strings). This behavior makes it impossible to pick arrays that have no
names. Fixing SetInputArrayToProcess to not ignore empty strings. Also
added a check in GetInputArrayToProcess to handle the case where no
array association was specified.

Change-Id: I3c3a9017ea014c2b8f844133956add72c1cf3e6d