Allow return of empty string values through placeholder resolver (3.2)

[TimHess]

Description

Patch to return the expected empty string instead of null when placeholder resolver is used

addresses #1132 in 3.2, will need to be applied to 4.0 as well.

Quality checklist

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[TimHess]

/azp run Steeltoe.All

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

100.0% Coverage
0.0% Duplication

[bart-vmware]

LGTM