When adding dynamic properties, fieldName dictionary name not set

Dapper/SqlMapper.cs

@@ -1234,6 +1234,7 @@ internal int AddField(string name)
                 if (fieldNameLookup.ContainsKey(name)) throw new InvalidOperationException("Field already exists: " + name);
                 int oldLen = fieldNames.Length;
                 Array.Resize(ref fieldNames, oldLen + 1); // yes, this is sub-optimal, but this is not the expected common case
+                fieldNames[oldLen] = name;
                 fieldNameLookup[name] = oldLen;
                 return oldLen;
             }