I may be being stupid, but is there a logic error here:

public String interpolate(String string, Object... params) {
 if ( params.length>10 )
 {
 throw new IllegalArgumentException("more than 10 parameters");
 }
 if ( string.indexOf('#')>=0 )
 {
 string = interpolateExpressions(string, params);
 }
 if ( params.length>1 && string.indexOf('{')>=0 )
 {
 string = new MessageFormat(string, Locale.instance()).format(params);
 }
 return string;
}

if ( params.length>1 && string.indexOf('{')>=0 )

if ( params.length>0 && string.indexOf('{')>=0 )