IsGenericMatrixRep does not work with RankMat #6642

gap> M := Matrix( IsGenericMatrixRep, GF(2), Z(2) * [ [ 1, 0 ], [ 0, 1 ] ] );;
gap> RankMat( M );
Error, row access unsupported; use M[i,j] or RowsOfMatrix(M)
Stack trace:
*[1] ErrorNoReturn( "row access unsupported; use M[i,j] or RowsOfMatrix(M)" );
   @ /home/peter/gap/gap/lib/matobjgeneric.gi:126
 [2] row := mat[i];
   @ /home/peter/gap/gap/lib/matrix.gi:2601
 [3] SemiEchelonMatDestructive( mat )
   @ /home/peter/gap/gap/lib/matrix.gi:2557
 [4] RankMatDestructive( MutableCopyMatrix( mat ) )
   @ /home/peter/gap/gap/lib/matrix.gi:2567
<function "RankMatrix generic method for matrices">( <arguments> )
 called from read-eval loop at *stdin*:2
you can enter 'quit;' to quit to outer loop

gap> M := Matrix( IsPlistMatrixRep, GF(2), Z(2) * [ [ 1, 0], [ 0, 1 ] ]);;
gap> RankMat(M);
2