Fix lock create and delete if parent-resource-path is None

[brendandburns]

@tjprescott

Part of #2694

[codecov-io]

Codecov Report

Merging #2742 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2742   +/-   ##
=======================================
  Coverage   61.16%   61.16%           
=======================================
  Files         480      480           
  Lines       25710    25710           
  Branches     3888     3888           
=======================================
  Hits        15725    15725           
+ Misses       9101     9060   -41     
- Partials      884      925   +41

Impacted Files	Coverage Δ
...ource/azure/cli/command_modules/resource/custom.py	54.7% <ø> (ø)	⬆️
...rce/azure/cli/command_modules/resource/commands.py	82.43% <0%> (ø)	⬆️
...e-cli-iot/azure/cli/command_modules/iot/_params.py	95.74% <0%> (ø)	⬆️
...cli-vm/azure/cli/command_modules/vm/_validators.py	68.5% <0%> (ø)	⬆️
...e-cli-acr/azure/cli/command_modules/acr/_format.py	38.88% <0%> (ø)	⬆️
...li-role/azure/cli/command_modules/role/commands.py	86.95% <0%> (ø)	⬆️
...re-cli-vm/azure/cli/command_modules/vm/commands.py	90.47% <0%> (ø)	⬆️
...e-cli-acs/azure/cli/command_modules/acs/_params.py	67.92% <0%> (ø)	⬆️
...gure/azure/cli/command_modules/configure/_utils.py	28.57% <0%> (ø)	⬆️
...e/azure/cli/command_modules/appservice/commands.py	89.7% <0%> (ø)	⬆️
... and 14 more

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