added validators

lib/service/validators.dart

@@ -12,3 +12,17 @@ String? dateTimeValidator(String? value) {
 
   return DateTime.tryParse(value) != null ? null : 'Not a date format';
 }
+
+String? coordinatesValidator(String? value) {
+  if (value == null || value.isEmpty) return null;
+
+  if (RegExp(r'^\d+\.?\d*, *\d+\.?\d*$').hasMatch(value)) {
+    return null;
+  }
+  return 'Not a valid coordinate format';
+}
+
+String? notEmptyValidator(String? value) {
+  if (value != null && value.isNotEmpty) return null;
+  return 'Can\'t be empty';
+}