Error with Matlab Coder and MatchFeatures function

hello, I try to generate C code for the function below

    % code
function indexPairs = matchFeatures_c(Model_Features,Features,unique,metric,MaxRation,MatchThreshold)%#codegen

 indexPairs = matchFeatures(Model_Features,Features,'unique',unique,...
        'metric',metric,...
        'MaxRatio',MaxRatio,...
        'MatchThreshold',MatchThreshold,...
        'method','approximate');%'Exhaustive') ;

this function is compatible with Code Generation according to the documentation :" Generates portable C code using a C++ compiler that links to user-provided OpenCV (Version 2.4.9) libraries when not using the Exhaustive method"

With the Coder app i always have this error :

1 findApproximateNearestNeighbors 70 This assignment writes a 'single' value into a 'int32' type. Code generation does not support changing types through assignment. Check preceding assignments or input type specifications for type mismatches.

how can i fix it?

kind regards Cédric