When creating a response we type check that the user has passed the
correct type to content and text, however we check this based on whether
the value is True and not whether it has been passed at all which means
that the empty string of the wrong type can incorrectly pass through
this check.
Fix this check to test the empty string.
Anyone relying on this passing will be caught with a more confusing
TypeError later and so this should be backwards compatible.
Change-Id: I826da9b7fd83bb88af50e4a96a5e6358ee35e4b2
Closes-Bug: #1647880
86fb33d13d