protected boolean containsProperty(String alias) {
		String k = resolveKey(alias);
		return k == null ? false : resolver.containsProperty(k);
	}
protected boolean containsProperty ( String alias ) { String k = resolveKey ( alias ) ; return k == null ? false : resolver . containsProperty ( k ) ; }
Return whether the given property alias has at least one property key
that is available for resolution, i.e., the value for the given key is
not {@code null}.

@param alias
the property alias to resolve
@return true if property exists, false otherwise