Add nil check for SSL certificate file paths (#1027) #4918

Job	Run time
Build Unsigned Snapshot	2m 2s
Lint	4m 35s
Unit tests with race condition detection	2m 45s
Performance Tests	4m 51s
Unit Tests	2m 18s
Integration Tests (ubuntu, 22.04)	9m 47s
Load Tests	4m 43s
Integration Tests - Official Plus Images (alpine, 3.20, r32, alpine, /nginx-plus/agent)	6m 25s
Integration Tests - Official OSS Images (bookworm, stable, debian)	6m 27s
Integration Tests - Official Plus Images (alpine, 3.19, r31, alpine, /nginx-plus/agent)	6m 36s
Integration Tests (redhatenterprise, 9)	9m 2s
Integration Tests - Official Plus Images (debian, bookworm, r32, debian, /nginx-plus/agent)	6m 48s
Integration Tests - Official OSS Images (bookworm, mainline, debian)	6m 45s
Integration Tests (alpine, 3.19)	6m 59s
Integration Tests - Official Plus Images (debian, bookworm, r31, debian, /nginx-plus/agent)	6m 34s
Integration Tests - Official OSS Images (alpine, stable, alpine)	6m 19s
Integration Tests - Official OSS Images (alpine, mainline, alpine)	6m 12s
Publish NGINX Agent v3 packages / Set workflow variables	3s
Publish NGINX Agent v3 packages / Update Release Draft	8s
Publish NGINX Agent v3 packages / Tag Release	2s
Publish NGINX Agent v3 packages / Upload packages	18m 19s
Publish NGINX Agent v3 packages / Merge release branch back into V3 branch	0s
	1h 57m 40s

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