panic: reflect: call of reflect.flag.mustBeExported on zero Value

[lnxbil]

Hi everyone,

I'm in the progress of migrating a project from perl to go and have problems with a previously working JSON schema file with conflate. I first tried gojsonschema and the schema was valid there, but had no default value integration, so I turned to conflate.

I ran into a panic (with my code and the conflate binary)

$ ~/go/bin/conflate -data testdata/data.yaml -schema schema/data.schema.json -validate -defaults
panic: reflect: call of reflect.flag.mustBeExported on zero Value

goroutine 1 [running]:
reflect.flag.mustBeExportedSlow(0x0)
        /usr/local/Cellar/go/1.13.4/libexec/src/reflect/value.go:222 +0xad
reflect.flag.mustBeExported(...)
        /usr/local/Cellar/go/1.13.4/libexec/src/reflect/value.go:216
reflect.Value.Set(0x147fbe0, 0xc000267c50, 0x194, 0x0, 0x0, 0x0)
        /usr/local/Cellar/go/1.13.4/libexec/src/reflect/value.go:1532 +0x56
github.com/miracl/conflate.applyDefaultsRecursive(0xc00026a850, 0xb, 0x14816e0, 0xc0001dab10, 0x1453340, 0xc000267c50, 0x14816e0, 0xc0001dade0, 0x0, 0x0)
        /Users/andreas/go/pkg/mod/github.com/miracl/[email protected]/schema.go:208 +0xa1f
github.com/miracl/conflate.applyObjectDefaults(0xc00026a780, 0x6, 0x14816e0, 0xc0001dab10, 0x14816e0, 0xc0001da0f0, 0xc0001dad80, 0x0, 0x0)
        /Users/andreas/go/pkg/mod/github.com/miracl/[email protected]/schema.go:247 +0x294
github.com/miracl/conflate.applyDefaultsRecursive(0xc00026a780, 0x6, 0x14816e0, 0xc0001dab10, 0x1453340, 0xc0002678e0, 0x14816e0, 0xc0001dad80, 0x0, 0x0)
        /Users/andreas/go/pkg/mod/github.com/miracl/[email protected]/schema.go:215 +0x959
github.com/miracl/conflate.applyObjectDefaults(0x150ad41, 0x1, 0x14816e0, 0xc0001dab10, 0x14816e0, 0xc0001da060, 0xc0001dab10, 0x10bd, 0x12bd)
        /Users/andreas/go/pkg/mod/github.com/miracl/[email protected]/schema.go:247 +0x294
github.com/miracl/conflate.applyDefaultsRecursive(0x150ad41, 0x1, 0x14816e0, 0xc0001dab10, 0x1453340, 0xc0000ba980, 0x14816e0, 0xc0001dab10, 0xc000188417, 0x0)
        /Users/andreas/go/pkg/mod/github.com/miracl/[email protected]/schema.go:215 +0x959
github.com/miracl/conflate.applyDefaults(0x1453340, 0xc0000ba980, 0x14816e0, 0xc0001dab10, 0x0, 0x0)
        /Users/andreas/go/pkg/mod/github.com/miracl/[email protected]/schema.go:160 +0x6c
github.com/miracl/conflate.(*Schema).ApplyDefaults(0xc000267820, 0x1453340, 0xc0000ba980, 0x0, 0x0)
        /Users/andreas/go/pkg/mod/github.com/miracl/[email protected]/schema.go:77 +0x54
github.com/miracl/conflate.(*Conflate).ApplyDefaults(...)
        /Users/andreas/go/pkg/mod/github.com/miracl/[email protected]/conflate.go:112
main.main()
        /Users/andreas/go/pkg/mod/github.com/miracl/[email protected]/conflate/main.go:72 +0x7f2

with this schema properties:

...
"host" : {
          "type": [ "string", "null" ],
          "description": "Hostname",
          "pattern": "^([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\\-]*[a-zA-Z0-9])$",
          "default": null
        },
...

If I change it to use only string (and allow the empty string in the validation), it works:

"host" : {
          "type": "string",
          "description": "Hostname",
          "pattern": "^([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\\-]*[a-zA-Z0-9]|)$",
          "default": ""
        },

It's not a big limitation, but I need to change my previously working schema file in order to get it to work with conflate.

Is this a bug worth noting?

Best, Andreas