get Attribute
Returns the value of an attribute found in this container, or null
if this container doesn't have it.
Return
the attribute value, or null if not found
Parameters
<T>
the type of the attribute
key
the attribute key
Returns the value of an attribute found in this container, or null
if this container doesn't have it.
the attribute value, or null if not found
the type of the attribute
the attribute key