See the simple testcase

    @Test
    public void testPreserveGenerics_PublicMethod() throws Exception {
        HintTest.create().setCaretMarker('|')
                .sourceLevel("1.6")
                .input("package test;\n"
                        + "public class Test {\n"
                        + "    public <T extends java.lang.Number> java.util.Set<T> fi|nd(){return null;};\n"
                        + "}\n")
                .run(MakePackageProtected.class)
                .findWarning("2:59-2:59:hint:" + Bundle.ERR_MakePackageProtected())
                .applyFix()
                .assertOutput("package test;\n"
                        + "public class Test {\n"
                        + "    <T extends java.lang.Number> java.util.Set<T> find(){return null;};\n"
                        + "}\n");
    }

MakePackageProtected hint simply invokes org.netbeans.spi.java.hints.support.FixFactory.changeModifiersFix/removeModifiersFix

ACTUAL:
Generics are not preserved, test fails
java.util.Set<T> find(){return null;};

EXPECTED:
Generics are preserved, test succeeds
<T extends java.lang.Number> java.util.Set<T> find(){return null;};

Reproduction: 
* Checkout https://github.com/markiewb/nb-additional-hints.git Branch feature/issue61-changemodifiersremovesgenerics
* test: https://github.com/markiewb/nb-additional-hints/commit/b6891a9f740027c4c17ea8251a2b0e0116b04e52
* hint: https://raw.githubusercontent.com/markiewb/nb-additional-hints/feature/issue61-changemodifiersremovesgenerics/src/main/java/de/markiewb/netbeans/plugins/hints/modifiers/MakePackageProtected.java