#vulnerable code 
                                public boolean matches() {

        // check & collect generic types.
        List<? extends VariableElement> candidateParameters = candidateMethod.getExecutable().getParameters();
        if ( candidateParameters.size() == parameters.length ) {
            for ( int i = 0; i < parameters.length; i++ ) {
                TypeMatcher parameterMatcher = new TypeMatcher();
                typesMatch = parameterMatcher.visit( candidateParameters.get( i ).asType(),
                        parameters[i].getTypeMirror() );
                if ( !typesMatch ) {
                    break;
                }
            }
        }
        else {
            typesMatch = false;
        }

        // check return type
        if ( typesMatch ) {
            TypeMirror candidateReturnType = candidateMethod.getExecutable().getReturnType();
            TypeMatcher returnTypeMatcher = new TypeMatcher();
            typesMatch = returnTypeMatcher.visit( candidateReturnType, returnType.getTypeMirror() );
        }

        // check if all type parameters are indeed mapped
        if ( candidateMethod.getExecutable().getTypeParameters().size() != this.genericTypesMap.size() ) {
            typesMatch = false;
        }
        else {
            // check if all entries are in the bounds
            for (Map.Entry<TypeVariable, TypeMirror> entry : genericTypesMap.entrySet()) {
                if (!isWithinBounds( entry.getValue(), getTypeParamFromCandite( entry.getKey() ) ) ) {
                    // checks if the found Type is in bounds of the TypeParameters bounds.
                    typesMatch = false;
                }
            }
        }
        return typesMatch;
    } 
                            #location 33 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public boolean matches() {
        // check & collect generic types.
        List<? extends VariableElement> candidateParameters = candidateMethod.getExecutable().getParameters();

        if ( candidateParameters.size() != 1 ) {
            typesMatch = false;
        }
        else {
            TypeMatcher parameterMatcher = new TypeMatcher();
            typesMatch = parameterMatcher.visit(
                candidateParameters.iterator().next().asType(),
                parameter.getTypeMirror()
            );
        }

        // check return type
        if ( typesMatch ) {
            TypeMirror candidateReturnType = candidateMethod.getExecutable().getReturnType();
            TypeMatcher returnTypeMatcher = new TypeMatcher();
            typesMatch = returnTypeMatcher.visit( candidateReturnType, returnType.getTypeMirror() );
        }

        // check if all type parameters are indeed mapped
        if ( candidateMethod.getExecutable().getTypeParameters().size() != this.genericTypesMap.size() ) {
            typesMatch = false;
        }
        else {
            // check if all entries are in the bounds
            for (Map.Entry<TypeVariable, TypeMirror> entry : genericTypesMap.entrySet()) {
                if (!isWithinBounds( entry.getValue(), getTypeParamFromCandidate( entry.getKey() ) ) ) {
                    // checks if the found Type is in bounds of the TypeParameters bounds.
                    typesMatch = false;
                }
            }
        }
        return typesMatch;
    }