Returns the SecurityManager instance that should be used to back the constructed {@link Subject} instance or
{@code null} if one has not yet been provided to this context.
@return the SecurityManager instance that should be used to back the constructed {@link Subject} instance or
{@code null} if one has not yet been provided to this context.
Returns the SecurityManager instance that should be used to back the constructed {@link Subject} instance or {@code null} if one has not yet been provided to this context.
@return the SecurityManager instance that should be used to back the constructed {@link Subject} instance or {@code null} if one has not yet been provided to this context.