private static TypeInfo generateEnumTypeInfo(Schema schema) {
    assert schema.getType().equals(Schema.Type.ENUM);

    return TypeInfoFactory.getPrimitiveTypeInfo("string");
  }
Generate a TypeInfo for an Avro Map.  This is made slightly simpler in that
Avro only allows maps with strings for keys.
serde/src/java/org/apache/hadoop/hive/serde2/avro/SchemaToTypeInfo.java