Resolve test failures due to NumPy 1.25

[lbianchi-lbl]

Resolves #1151

(replace this with the issue # fixed or addressed, if no issue exists then a brief statement of what this PR does)

Summary/Motivation:

Changes proposed in this PR:

• Add an isinstance() check before comparing with empty string to avoid NumPy error

Legal Acknowledgement

By contributing to this software project, I agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the copyright and license terms described in the LICENSE.md file at the top level of this directory.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (d70d4f5) 37.23% compared to head (fb70738) 37.23%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1152   +/-   ##
=======================================
  Coverage   37.23%   37.23%           
=======================================
  Files         160      160           
  Lines       36343    36343           
  Branches     5944     5944           
=======================================
  Hits        13531    13531           
  Misses      21730    21730           
  Partials     1082     1082           

Impacted Files	Coverage Δ
foqus_lib/framework/uq/SampleData.py	52.89% <100.00%> (ø)

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[sotorrio1]

looks good to me