From d56e2d794b2ac6a36ab7a499c21345a08e58b2c0 Mon Sep 17 00:00:00 2001
From: Adnan Maolood <me@adnano.co>
Date: Wed, 26 Jan 2022 07:09:28 -0500
Subject: [PATCH] valid: Add NullableString

Add a NullableString method to allow users to differentiate between the
absence of a field and an explicitly provided null value.
---
 valid/valid.go | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/valid/valid.go b/valid/valid.go
index 13466b80f22fbb583022e84e088ca50f1e0e358c..89f81e1299f550aaff8f748fdf1c9bb753af2b56 100644
--- a/valid/valid.go
+++ b/valid/valid.go
@@ -91,6 +91,34 @@ func (valid *Validation) OptionalString(name string, fn func(s string)) {
 	}
 }
 
+// Fetches a nullable string from the validation context, which must have an
+// input registered. If the field is not present, the callback is not run. If
+// present, but null, the function is called with null set to true. Otherwise,
+// the function is called with the string for the user to conduct further
+// validation with.
+func (valid *Validation) NullableString(name string, fn func(s *string)) {
+	if valid.input == nil {
+		panic("Attempted to validate fields without input")
+	}
+	if o, ok := valid.input[name]; ok {
+		var val *string
+		if o != nil {
+			switch s := o.(type) {
+			case string:
+				val = &s
+			case *string:
+				val = s
+			default:
+				valid.
+					Error("Expected %s to be a string", name).
+					WithField(name)
+				return
+			}
+		}
+		fn(val)
+	}
+}
+
 // Fetches a boolean from the validation context, which must have an input
 // registered. If the field is not present, the callback is not run. If
 // present, but not a boolean, an error is recorded. Otherwise, the function is