Unify default values of inputs (terraform-docs#97)

Author: metmajer

examples/variables.tf

@@ -1,5 +1,9 @@
 variable unquoted {}
 
+variable "string-3" {
+  default = ""
+}
+
 variable "string-2" {
   description = "It's string number two."
   type        = "string"

internal/pkg/doc/doc.go

@@ -21,12 +21,6 @@ type Doc struct {
 	Outputs []Output
 }
 
-// Value represents a Terraform value.
-type Value struct {
-	Type  string
-	Value interface{}
-}
-
 // HasComment indicates if the document has a comment.
 func (d *Doc) HasComment() bool {
 	return len(d.Comment) > 0
@@ -42,6 +36,17 @@ func (d *Doc) HasOutputs() bool {
 	return len(d.Outputs) > 0
 }
 
+// Value represents a Terraform value.
+type Value struct {
+	Type  string
+	Value interface{}
+}
+
+// IsAggregateType indicates if a Terraform value is an aggregate type.
+func (v Value) IsAggregateType() bool {
+	return v.Type == "list" || v.Type == "map"
+}
+
 // CreateFromPaths creates a new document from a list of file or directory paths.
 func CreateFromPaths(paths []string) (*Doc, error) {
 	names := make([]string, 0)