public FileTree getSource() {
        return super.getSource();
    }

    /**
     * Configures the java compiler to be used to compile the Java source.
     *
     * @see org.gradle.jvm.toolchain.JavaToolchainSpec
     * @since 6.7
     */
    @Nested
    public Property<JavaCompiler> getJavaCompiler() {
        return javaCompiler;
    }

    /**

Even though these properties can be configured independently, the configuration must follow certain rules in order to form a _valid_ specification.

A `JavaToolchainSpec` is considered _valid_ in two cases:

1. when no properties have been set, i.e. the specification is _empty_;
2. when `languageVersion` has been set, optionally followed by setting any other property.