Could not determine the type of ''.

[Alessandro-Barbieri]

When compiling from source on gentoo I get this

==> cmake /opt/ros/ros_catkin_ws/src/pr2_common/pr2_description -DCATKIN_DEVEL_PREFIX=/opt/ros/ros_catkin_ws/devel_isolated/pr2_description -DCMAKE_INSTALL_PREFIX=/opt/ros/indigo -DCMAKE_BUILD_TYPE=Release -DSETUPTOOLS_ARG_EXTRA= -DSETUPTOOLS_DEB_LAYOUT=OFF -G Unix Makefiles in '/opt/ros/ros_catkin_ws/build_isolated/pr2_description'
-- The C compiler identification is GNU 4.8.4
-- The CXX compiler identification is GNU 4.8.4
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Using CATKIN_DEVEL_PREFIX: /opt/ros/ros_catkin_ws/devel_isolated/pr2_description
-- Using CMAKE_PREFIX_PATH: /opt/ros/indigo
-- This workspace overlays: /opt/ros/indigo
-- Found PythonInterp: /usr/bin/python (found version "2.7.9") 
-- Using PYTHON_EXECUTABLE: /usr/bin/python
-- Using default Python package layout
-- Found PY_em: /usr/lib/python2.7/site-packages/em.pyc  
-- Using empy: /usr/lib/python2.7/site-packages/em.pyc
-- Using CATKIN_ENABLE_TESTING: ON
-- Call enable_testing()
-- Using CATKIN_TEST_RESULTS_DIR: /opt/ros/ros_catkin_ws/build_isolated/pr2_description/test_results
-- Found gtest: gtests will be built
-- Using Python nosetests: /usr/bin/nosetests
-- catkin 0.6.14
-- Configuring done
-- Generating done
CMake Warning:
  Manually-specified variables were not used by the project:

    SETUPTOOLS_ARG_EXTRA


-- Build files have been written to: /opt/ros/ros_catkin_ws/build_isolated/pr2_description
==> make -j1 -l1 in '/opt/ros/ros_catkin_ws/build_isolated/pr2_description'
Scanning dependencies of target media_files
[  0%] Generating /opt/ros/ros_catkin_ws/src/pr2_common/pr2_description/meshes/gripper_v0/convex/upper_finger_l.obj

DATA_READ - Fatal error!
  Could not determine the type of ''.

COMMAND_LINE - Fatal error!
  Failure while reading input data.
CMakeFiles/media_files.dir/build.make:287: set di istruzioni per l'obiettivo "/opt/ros/ros_catkin_ws/src/pr2_common/pr2_description/meshes/gripper_v0/convex/upper_finger_l.obj" non riuscito
make[2]: *** [/opt/ros/ros_catkin_ws/src/pr2_common/pr2_description/meshes/gripper_v0/convex/upper_finger_l.obj] Errore 1
CMakeFiles/Makefile2:282: set di istruzioni per l'obiettivo "CMakeFiles/media_files.dir/all" non riuscito
Makefile:126: set di istruzioni per l'obiettivo "all" non riuscito
<== Failed to process package 'pr2_description': 
  Command '['/opt/ros/indigo/env.sh', 'make', '-j1', '-l1']' returned non-zero exit status 2

Reproduce this error by running:
==> cd /opt/ros/ros_catkin_ws/build_isolated/pr2_description && /opt/ros/indigo/env.sh make -j1 -l1

make[1]: *** [CMakeFiles/media_files.dir/all] Errore 2
make: *** [all] Errore 2
Command failed, exiting.
./src/catkin/bin/catkin_make_isolated --install --install-space  

but I don't know what's wrong.