More minor tweaks (#277)

Signed-off-by: Steve Coffman <steve@khanacademy.org>

ast/path.go

@@ -18,6 +18,9 @@ var _ PathElement = PathIndex(0)
 var _ PathElement = PathName("")
 
 func (path *Path) String() string {
+	if path == nil {
+		return ""
+	}
 	var str bytes.Buffer
 	for i, v := range *path {
 		switch v := v.(type) {

gqlerror/error.go

@@ -72,6 +72,13 @@ func (err *Error) Unwrap() error {
 	return err.err
 }
 
+func (err *Error) AsError() error {
+	if err == nil {
+		return nil
+	}
+	return err
+}
+
 func (errs List) Error() string {
 	var buf bytes.Buffer
 	for _, err := range errs {

parser/schema.go

@@ -6,6 +6,18 @@ import (
 	"github.com/vektah/gqlparser/v2/lexer"
 )
 
+func ParseSchemas(inputs ...*Source) (*SchemaDocument, error) {
+	sd := &SchemaDocument{}
+	for _, input := range inputs {
+		inputAst, err := ParseSchema(input)
+		if err != nil {
+			return nil, err
+		}
+		sd.Merge(inputAst)
+	}
+	return sd, nil
+}
+
 func ParseSchema(source *Source) (*SchemaDocument, error) {
 	p := parser{
 		lexer: lexer.New(source),
@@ -25,18 +37,6 @@ func ParseSchema(source *Source) (*SchemaDocument, error) {
 	return sd, nil
 }
 
-func ParseSchemas(inputs ...*Source) (*SchemaDocument, error) {
-	sd := &SchemaDocument{}
-	for _, input := range inputs {
-		inputAst, err := ParseSchema(input)
-		if err != nil {
-			return nil, err
-		}
-		sd.Merge(inputAst)
-	}
-	return sd, nil
-}
-
 func (p *parser) parseSchemaDocument() *SchemaDocument {
 	var doc SchemaDocument
 	doc.Position = p.peekPos()