fix NPEs (#1170)

specs/spring-cloud-contract-spec-java/src/main/java/org/springframework/cloud/contract/spec/internal/OptionalProperty.java

@@ -44,8 +44,15 @@ public class OptionalProperty implements Serializable, CanBeDynamic {
 	}
 
 	public String value() {
-		return this.value instanceof RegexProperty
-				? ((RegexProperty) this.value).pattern() : this.value.toString();
+		if (this.value == null) {
+			return "";
+		}
+		else if (this.value instanceof RegexProperty) {
+			return ((RegexProperty) this.value).pattern();
+		}
+		else {
+			return this.value.toString();
+		}
 	}
 
 	protected Pattern optionalPatternValue() {

spring-cloud-contract-verifier/src/main/groovy/org/springframework/cloud/contract/verifier/builder/QueryParamsResolver.java

@@ -34,12 +34,12 @@ interface QueryParamsResolver {
 			return resolveParamValue(((OptionalProperty) value).optionalPattern());
 		}
 		else if (value instanceof MatchingStrategy) {
-			return ((MatchingStrategy) value).getServerValue().toString();
+			return resolveParamValue(((MatchingStrategy) value).getServerValue());
 		}
 		else if (value instanceof DslProperty) {
 			return resolveParamValue(((DslProperty) value).getServerValue());
 		}
-		return value.toString();
+		return value == null ? "null" : value.toString();
 	}
 
 }

spring-cloud-contract-verifier/src/test/groovy/org/springframework/cloud/contract/verifier/builder/QueryParamsResolverSpec.groovy

@@ -0,0 +1,84 @@
+package org.springframework.cloud.contract.verifier.builder
+
+import org.springframework.cloud.contract.spec.internal.DslProperty
+import org.springframework.cloud.contract.spec.internal.MatchingStrategy
+import org.springframework.cloud.contract.spec.internal.OptionalProperty
+import org.springframework.cloud.contract.spec.internal.QueryParameter
+import org.springframework.cloud.contract.spec.internal.RegexProperty
+import spock.lang.Specification
+
+import java.util.regex.Pattern
+
+class QueryParamsResolverSpec extends Specification {
+
+	def 'should return serverValue for QueryParameter'() {
+		given:
+			Object parameter = new QueryParameter("some_param", dslProperty)
+		when:
+			String resolved = new QueryParamsResolver() {}.resolveParamValue(parameter)
+		then:
+			resolved == expected
+		where:
+			dslProperty                                 | expected
+			new DslProperty<String>("client", "server") | "server"
+			new DslProperty<String>(null, "server")     | "server"
+			new DslProperty<String>("client", null)     | "null"
+			new DslProperty<String>(null, null)         | "null"
+	}
+
+	def 'should return optionalPattern for OptionalProperty'() {
+		given:
+			Object parameter = new OptionalProperty(value)
+		when:
+			String resolved = new QueryParamsResolver() {}.resolveParamValue(parameter)
+		then:
+			resolved == expected
+		where:
+			value                                          | expected
+			"server"                                       | "(server)?"
+			null                                           | "()?"
+			new RegexProperty(Pattern.compile(".*"))       | "(.*)?"
+			new RegexProperty(null, Pattern.compile(".*")) | "(.*)?"
+			new RegexProperty(Pattern.compile(".*"), null) | "(.*)?"
+			new RegexProperty("", Pattern.compile(".*"))   | "(.*)?"
+			new RegexProperty(Pattern.compile(".*"), "")   | "(.*)?"
+	}
+
+	def 'should return serverValue for MatchingStrategy'() {
+		given:
+			Object parameter = new MatchingStrategy(value, MatchingStrategy.Type.EQUAL_TO)
+		when:
+			String resolved = new QueryParamsResolver() {}.resolveParamValue(parameter)
+		then:
+			resolved == expected
+		where:
+			value                                       | expected
+			"server"                                    | "server"
+			null                                        | "null"
+			new DslProperty<String>("client", "server") | "server"
+			new DslProperty<String>(null, "server")     | "server"
+			new DslProperty<String>("client", null)     | "null"
+			new DslProperty<String>(null, null)         | "null"
+	}
+
+	def 'should return serverValue for DslProperty'() {
+		when:
+			String resolved = new QueryParamsResolver() {}.resolveParamValue(parameter)
+		then:
+			resolved == expected
+		where:
+			parameter                                   | expected
+			new DslProperty<String>("client", "server") | "server"
+			new DslProperty<String>(null, "server")     | "server"
+			new DslProperty<String>("client", null)     | "null"
+			new DslProperty<String>(null, null)         | "null"
+	}
+
+	def 'should return \"null\" for null'() {
+		when:
+			String resolved = new QueryParamsResolver() {}.resolveParamValue(null)
+		then:
+			resolved == "null"
+	}
+
+}