Handle PostgreSQL chars correctly (#1326)

* Handle char correctly

* Add PostgreSQL char test

* Test for string before testing for char

Dapper.Tests/Providers/PostgresqlTests.cs

@@ -56,6 +56,28 @@ public void TestPostgresqlArrayParameters()
             }
         }
 
+        private class CharTable
+        {
+            public int Id { get; set; }
+            public char CharColumn { get; set; }
+        }
+
+        [FactPostgresql]
+        public void TestPostgresqlChar()
+        {
+            using (var conn = GetOpenNpgsqlConnection())
+            {
+                var transaction = conn.BeginTransaction();
+                conn.Execute("create table chartable (id serial not null, charcolumn \"char\" not null);");
+                conn.Execute("insert into chartable(charcolumn) values('a');");
+
+                var r = conn.Query<CharTable>("select * from chartable");
+                Assert.Single(r);
+                Assert.Equal('a', r.Single().CharColumn);
+                transaction.Rollback();
+            }
+        }
+
         [AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
         public class FactPostgresqlAttribute : FactAttribute
         {

Dapper/SqlMapper.cs

@@ -1877,8 +1877,13 @@ public static char ReadChar(object value)
         {
             if (value == null || value is DBNull) throw new ArgumentNullException(nameof(value));
             var s = value as string;
-            if (s == null || s.Length != 1) throw new ArgumentException("A single-character was expected", nameof(value));
-            return s[0];
+            if (s == null)
+            {
+                var c = value as char?;
+                if (c != null) return c.Value;
+            }
+            else if (s.Length == 1) return s[0];
+            throw new ArgumentException("A single-character was expected", nameof(value));
         }
 
         /// <summary>
@@ -1892,8 +1897,13 @@ public static char ReadChar(object value)
         {
             if (value == null || value is DBNull) return null;
             var s = value as string;
-            if (s == null || s.Length != 1) throw new ArgumentException("A single-character was expected", nameof(value));
-            return s[0];
+            if (s == null)
+            {
+                var c = value as char?;
+                if (c != null) return c;
+            }
+            else if (s.Length == 1) return s[0];
+            throw new ArgumentException("A single-character was expected", nameof(value));
         }
 
         /// <summary>