public Node expectMember(String name) {
        return expectMember(name, () -> format("Missing expected member `%s`.", name));
    }
Gets the member with the given name.

@param name Name of the member to get.
@return Returns the node with the given member name.
@throws IllegalArgumentException when {@code memberName} is null.
@throws ExpectationNotMetException when {@code memberName} is not
 present in the members map.
smithy-model/src/main/java/software/amazon/smithy/model/node/ObjectNode.java