StringIndexOutOfBoundsException with multiple expressions

[rbygrave]

Failing test case

statusPageUrl=https://${eureka.instance.hostname}:${server.port}/status

java.lang.StringIndexOutOfBoundsException: begin 17, end 15, length 51

	at java.base/java.lang.String.checkBoundsBeginEnd(String.java:3720)
	at java.base/java.lang.String.substring(String.java:1909)
	at io.avaje.config.load.CoreExpressionEval$EvalBuffer.parseForDefault(CoreExpressionEval.java:164)
	at io.avaje.config.load.CoreExpressionEval$EvalBuffer.evalNext(CoreExpressionEval.java:209)
	at io.avaje.config.load.CoreExpressionEval$EvalBuffer.process(CoreExpressionEval.java:214)
	at io.avaje.config.load.CoreExpressionEval.eval(CoreExpressionEval.java:102)
	at io.avaje.config.load.CoreExpressionEval.eval(CoreExpressionEval.java:62)
	at io.avaje.config.load.LoadContext.evalAll(LoadContext.java:129)
	at io.avaje.config.load.Loader.eval(Loader.java:238)
	at io.avaje.config.load.LoaderTest.loadProperties(LoaderTest.java:72)