Build not working due to lack of JAVA7_HOME environment variable

Shrinkwrap nio2-api fails to compile, resulting in the following error:

[INFO] ------------------------------------------------------------------------
[INFO] Building ShrinkWrap NIO.2 API 1.1.3-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] — maven-clean-plugin:2.4.1:clean (default-clean) @ shrinkwrap-api-nio2 —
[INFO] Deleting C:\source\external\shrinkwrap\api-nio2\target
[INFO]
[INFO] — maven-enforcer-plugin:1.0:enforce (enforce-java-version) @ shrinkwrap-api-nio2 —
[INFO]
[INFO] — maven-enforcer-plugin:1.0:enforce (enforce-maven-version) @ shrinkwrap-api-nio2 —
[INFO]
[INFO] — maven-enforcer-plugin:1.0:enforce (enforce-maven-environment) @ shrinkwrap-api-nio2 —
[INFO]
[INFO] — maven-resources-plugin:2.5:resources (default-resources) @ shrinkwrap-api-nio2 —
[debug] execute contextualize
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory C:\source\external\shrinkwrap\api-nio2\src\main\resources
[INFO]
[INFO] — maven-compiler-plugin:2.3.2:compile (default-compile) @ shrinkwrap-api-nio2 —
[INFO] Compiling 4 source files to C:\source\external\shrinkwrap\api-nio2\target\classes
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] Failure executing javac, but could not parse the error:
The system cannot find the path specified.

After some digging into this, it turned out this error was down to a missing environment variable JAVA7_HOME. This is not obvious from the error message.

Currently in the shrinkwrap parent pom.xml there is a check for the JAVA5_HOME. Could an additional check be added at the same point for JAVA7_HOME?