Prevent null reference when reading boot_diagnostics settings.

[rrudduck]

I ran into this scenario on a few virtual machines. The rest response contained this:

2016/11/21 22:12:40 [DEBUG] plugin: terraform.exe: "diagnosticsProfile": {
2016/11/21 22:12:40 [DEBUG] plugin: terraform.exe: "bootDiagnostics": {
2016/11/21 22:12:40 [DEBUG] plugin: terraform.exe: "enabled": false
2016/11/21 22:12:40 [DEBUG] plugin: terraform.exe: }
2016/11/21 22:12:40 [DEBUG] plugin: terraform.exe: },

Which caused the following panic in 0.7.10 and 0.7.11:

2016/11/21 21:48:10 [DEBUG] plugin: terraform.exe: panic: runtime error: invalid memory address or nil pointer dereference
2016/11/21 21:48:10 [DEBUG] plugin: terraform.exe: [signal 0xc0000005 code=0x0 addr=0x0 pc=0xb1e6cb]
2016/11/21 21:48:10 [DEBUG] plugin: terraform.exe:
2016/11/21 21:48:10 [DEBUG] plugin: terraform.exe: goroutine 3642 [running]:
2016/11/21 21:48:10 [DEBUG] plugin: terraform.exe: panic(0x2a99da0, 0xc04200e090)
2016/11/21 21:48:10 [DEBUG] plugin: terraform.exe: /opt/go/src/runtime/panic.go:500 +0x1af
2016/11/21 21:48:10 [DEBUG] plugin: terraform.exe: github.com/hashicorp/terraform/builtin/providers/azurerm.resourceArmVirtualMachineRead(0xc042e762a0, 0x2cce4e0, 0xc042061a00, 0x0, 0x17)
2016/11/21 21:48:10 [DEBUG] plugin: terraform.exe: /opt/gopath/src/github.com/hashicorp/terraform/builtin/providers/azurerm/resource_arm_virtual_machine.go:613 +0xedb
2016/11/21 21:48:10 [DEBUG] plugin: terraform.exe: github.com/hashicorp/terraform/helper/schema.(*Resource).Refresh(0xc0422fcae0, 0xc042ee20f0, 0x2cce4e0, 0xc042061a00, 0xc0420422b0, 0x1, 0x18)

This fix handles this case by preventing the nil dereference in this case. I'm not sure why only a few VMs experienced the initial issue but this solved it for me.

[kwilczynski]

@rrudduck hi there! Nice catch! Thank you for that!

[stack72]

Hi @rrudduck

Thanks for the work here - nice guard clause :)

P.

[ghost]

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