Fix value method call on nil pointer (#111)

reflect.go

@@ -387,15 +387,15 @@ func (r *Reflector) reflectDefer(defName string, typeString refl.TypeString, rc
 }
 
 func (r *Reflector) checkTitle(v reflect.Value, s *Struct, schema *Schema) {
-	if vd, ok := v.Interface().(Described); ok {
+	if vd, ok := safeInterface(v).(Described); ok {
 		schema.WithDescription(vd.Description())
 	}
 
 	if s != nil && s.Description != nil {
 		schema.WithDescription(*s.Description)
 	}
 
-	if vt, ok := v.Interface().(Titled); ok {
+	if vt, ok := safeInterface(v).(Titled); ok {
 		schema.WithTitle(vt.Title())
 	}
 
@@ -532,7 +532,7 @@ func (r *Reflector) reflect(i interface{}, rc *ReflectContext, keepType bool, pa
 		}
 	}
 
-	if preparer, ok := v.Interface().(Preparer); ok {
+	if preparer, ok := safeInterface(v).(Preparer); ok {
 		err := preparer.PrepareJSONSchema(sp)
 
 		return schema, err
@@ -555,8 +555,16 @@ func checkTextMarshaler(t reflect.Type, schema *Schema) bool {
 	return false
 }
 
+func safeInterface(v reflect.Value) interface{} {
+	if v.Kind() == reflect.Ptr && !v.Elem().IsValid() {
+		v = reflect.New(v.Type())
+	}
+
+	return v.Interface()
+}
+
 func (r *Reflector) applySubSchemas(v reflect.Value, rc *ReflectContext, schema *Schema) error {
-	vi := v.Interface()
+	vi := safeInterface(v)
 
 	if e, ok := vi.(OneOfExposer); ok {
 		var schemas []SchemaOrBool

reflect_test.go

@@ -1949,3 +1949,38 @@ func TestReflector_Reflect_ptrDefault(t *testing.T) {
 	  "type":"object"
 	}`, s)
 }
+
+func TestReflector_Reflect_nilPreparer(t *testing.T) {
+	var o *Org
+
+	r := jsonschema.Reflector{}
+
+	s, err := r.Reflect(o)
+	require.NoError(t, err)
+	assertjson.EqMarshal(t, `{
+	  "definitions":{
+		"JsonschemaGoTestEnumed":{"enum":["foo","bar"],"type":"string"},
+		"JsonschemaGoTestPerson":{
+		  "title":"Person","required":["lastName"],
+		  "properties":{
+			"birthDate":{"type":"string","format":"date"},
+			"createdAt":{"type":"string","format":"date-time"},
+			"date":{"type":"string","format":"date"},
+			"deathDate":{"type":["null","string"],"format":"date"},
+			"deletedAt":{"type":["null","string"],"format":"date-time"},
+			"enumed":{"$ref":"#/definitions/JsonschemaGoTestEnumed"},
+			"enumedPtr":{"$ref":"#/definitions/JsonschemaGoTestEnumed"},
+			"firstName":{"type":"string"},"height":{"type":"integer"},
+			"lastName":{"type":"string"},"meta":{},
+			"role":{"description":"The role of person.","type":"string"}
+		  },
+		  "type":"object"
+		}
+	  },
+	  "properties":{
+		"chiefOfMorale":{"$ref":"#/definitions/JsonschemaGoTestPerson"},
+		"employees":{"items":{"$ref":"#/definitions/JsonschemaGoTestPerson"},"type":"array"}
+	  },
+	  "type":"object"
+	}`, s)
+}