This commit introduces a conditional call in
AbstractJackson2HttpMessageConverter#getJavaType() in order to avoid
calling TypeFactory#constructType() with a null contextClass parameter,
since this is not supported by Jackson 2.7 anymore.
It allows to use Spring Framework 4.2.x with Jackson 2.7.1+ for most use
cases, but with some limitations. For example, with Jackson 2.7
TypeVariable resolution from method parameters does not work.
As a consequence, after this commit Spring Framework 4.2.x still fully
supports Jackson up to version 2.6, but improves Jackson 2.7 compatibility.
Full support for Jackson 2.7 is provided as of Spring Framework 4.3.x.
Issue: SPR-13853
09db26af2b