sandbox/src/main/java/org/robolectric/internal/bytecode/RobolectricGeneratorAdapter.java
public void pushDefaultReturnValueToStack(Type type) {
    if (type.equals(Type.BOOLEAN_TYPE)) {
      push(false);
    } else if (type.equals(Type.INT_TYPE) || type.equals(Type.SHORT_TYPE) || type.equals(Type.BYTE_TYPE) || type.equals(Type.CHAR_TYPE)) {
      push(0);
    } else if (type.equals(Type.LONG_TYPE)) {
      push(0L);
    } else if (type.equals(Type.FLOAT_TYPE)) {
      push(0f);
    } else if (type.equals(Type.DOUBLE_TYPE)) {
      push(0d);
    } else if (type.getSort() == ARRAY || type.getSort() == OBJECT) {
      loadNull();
    }
  }
public void pushDefaultReturnValueToStack(Type type) {
    if (type.equals(Type.BOOLEAN_TYPE)) {
      push(false);
    } else if (type.equals(Type.INT_TYPE) || type.equals(Type.SHORT_TYPE) || type.equals(Type.BYTE_TYPE) || type.equals(Type.CHAR_TYPE)) {
      push(0);
    } else if (type.equals(Type.LONG_TYPE)) {
      push(0L);
    } else if (type.equals(Type.FLOAT_TYPE)) {
      push(0f);
    } else if (type.equals(Type.DOUBLE_TYPE)) {
      push(0d);
    } else if (type.getSort() == ARRAY || type.getSort() == OBJECT) {
      loadNull();
    }
  }
Forces a return of a default value, depending on the method's return type

@param type The method's return type