Updated two argument `check_return_type` to work with one argument not a matrix (Issue #2101)
Updated two argument `check_return_type` to work with one argument not a matrix (Issue #2101)

stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math