tf-crash-null-provider-version

2019/05/30 08:41:41 [INFO] Terraform version: 0.12.0  
2019/05/30 08:41:41 [INFO] Go runtime version: go1.12.5
2019/05/30 08:41:41 [INFO] CLI args: []string{"/usr/local/bin/terraform", "apply"}
2019/05/30 08:41:41 [DEBUG] Attempting to open CLI config file: /Users/alistairhey/.terraformrc
2019/05/30 08:41:41 Loading CLI configuration from /Users/alistairhey/.terraformrc
2019/05/30 08:41:41 [INFO] CLI command args: []string{"apply"}
panic: value is unknown

goroutine 1 [running]:
github.com/hashicorp/terraform/vendor/github.com/zclconf/go-cty/cty.Value.AsString(...)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/vendor/github.com/zclconf/go-cty/cty/value_ops.go:1032
github.com/hashicorp/terraform/configs.decodeVersionConstraint(0xc000272f00, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/configs/version_constraint.go:48 +0x9bf
github.com/hashicorp/terraform/configs.decodeProviderBlock(0xc00046e340, 0x8, 0x27bf1a4, 0x8, 0xffffffffffffffff)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/configs/provider.go:55 +0x847
github.com/hashicorp/terraform/configs.(*Parser).loadConfigFile(0xc00000c040, 0xc000480619, 0x7, 0x0, 0x0, 0x0, 0x0, 0x1)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/configs/parser_config.go:82 +0x1015
github.com/hashicorp/terraform/configs.(*Parser).LoadConfigFile(...)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/configs/parser_config.go:22
github.com/hashicorp/terraform/configs.(*Parser).loadFiles(0xc00000c040, 0xc0005a00c0, 0x1, 0x1, 0x0, 0x1, 0x0, 0x0, 0x0, 0x0, ...)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/configs/parser_config_dir.go:76 +0x343
github.com/hashicorp/terraform/configs.(*Parser).LoadConfigDir(0xc00000c040, 0x27b81cd, 0x1, 0x0, 0x1, 0x0, 0xc00052f960)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/configs/parser_config_dir.go:36 +0x121
github.com/hashicorp/terraform/command.(*Meta).loadSingleModule(0xc000293ba0, 0x27b81cd, 0x1, 0xc00052f960, 0x22c6e4c, 0xc0000a6270, 0x1)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/command/meta_config.go:113 +0x136
github.com/hashicorp/terraform/command.(*Meta).loadBackendConfig(0xc000293ba0, 0xc000046064, 0x1e, 0x0, 0x0, 0x0, 0x0)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/command/meta_config.go:175 +0x43
github.com/hashicorp/terraform/command.(*ApplyCommand).Run(0xc000293ba0, 0xc0000be010, 0x0, 0x0, 0xc0001df060)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/command/apply.go:132 +0x13a5
github.com/hashicorp/terraform/vendor/github.com/mitchellh/cli.(*CLI).Run(0xc00027a000, 0xc00027a000, 0xc00052fd90, 0x1)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/vendor/github.com/mitchellh/cli/cli.go:255 +0x1f1
main.wrappedMain(0x0)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/main.go:223 +0xaff
main.realMain(0x0)
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/main.go:100 +0xb4
main.main()
        /private/tmp/terraform-20190523-61862-1w2ypr9/terraform-0.12.0/src/github.com/hashicorp/terraform/main.go:36 +0x3b