Revert "Unset config properties: System.getProperty should return default value or null" (#10094)

Tests are currently failing, need to be re-checked.

Reverts #10013

Author: niloc132

dev/core/src/com/google/gwt/dev/cfg/ConfigurationProperties.java

@@ -141,17 +141,6 @@ public List<String> getStrings(String key) {
     return properties.get(key);
   }
 
-  /**
-   * Returns all the values of a multi-valued configuration property, or null
-   * if not found.
-   *
-   * <p>A single-valued and unset configuration property will be returned as a list
-   * containing one null.
-   */
-  public List<String> getStringsOrNull(String key) {
-     return properties.get(key);
-  }
-
   /**
    * Reads a configuration property as a comma-separated list of strings.
    * It may be a single-valued or multi-valued property. If multi-valued,

dev/core/src/com/google/gwt/dev/jjs/impl/ResolvePermutationDependentValues.java

@@ -47,7 +47,6 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
-import java.util.Objects;
 import java.util.Set;
 
 /**
@@ -75,28 +74,21 @@ public void endVisit(JPermutationDependentValue x, Context ctx) {
     }
 
     private JExpression propertyValueExpression(JPermutationDependentValue x) {
-      List<String> propertyValues = props.getConfigurationProperties()
-          .getStringsOrNull(x.getRequestedValue());
-      if (propertyValues != null) {
+      List<String> propertyValues = props.getConfigurationProperties().getStrings(x.getRequestedValue());
+
+      String propertyValue = propertyValues.isEmpty() ? null : Joiner.on(",").join(propertyValues);
+
+      if (propertyValue != null) {
         // It is a configuration property.
-        // If no values are set, propertyValues is either empty (multivalued properties)
-        // or contains a single null (other properties).
-        if (propertyValues.stream().anyMatch(Objects::nonNull)) {
-          return program.getLiteral(x.getSourceInfo(),
-              Joiner.on(",").skipNulls().join(propertyValues));
-        }
-        if (x.getDefaultValueExpression() != null) {
-          return x.getDefaultValueExpression();
-        }
-        return program.getLiteralNull();
+        return program.getLiteral(x.getSourceInfo(), propertyValue);
       }
 
       if (isSoftPermutationProperty(x.getRequestedValue())) {
         JMethod method = getOrCreateSoftPropertyMethod(x.getSourceInfo(), x.getRequestedValue());
         return new JMethodCall(x.getSourceInfo(), null, method);
       }
 
-      String propertyValue = commonPropertyAndBindingInfo.getPropertyValue(x.getRequestedValue());
+      propertyValue = commonPropertyAndBindingInfo.getPropertyValue(x.getRequestedValue());
 
       if (propertyValue != null) {
         return program.getLiteral(x.getSourceInfo(), propertyValue);

user/test/com/google/gwt/dev/jjs/SystemGetPropertyTest.gwt.xml

@@ -33,6 +33,4 @@
   <set-property name="someOtherDynamicProperty" value="blue">
     <when-property-is name="collapsedProperty" value="two"/>
   </set-property>
-  <define-configuration-property name="configPropertyUnset" is-multi-valued="false"/>
-  <define-configuration-property name="multivaluedConfigPropertyUnset" is-multi-valued="true"/>
 </module>

user/test/com/google/gwt/dev/jjs/test/SystemGetPropertyTest.java

@@ -36,9 +36,5 @@ public void testBindingProperties() {
     String expectedResult = "safari".equals(System.getProperty("user.agent")) ?
         "InSafari" : "NotInSafari";
     assertEquals(expectedResult, System.getProperty("someDynamicProperty"));
-    assertEquals("foo", System.getProperty("configPropertyUnset", "foo"));
-    assertNull(System.getProperty("configPropertyUnset"));
-    assertEquals("foo", System.getProperty("multivaluedConfigPropertyUnset", "foo"));
-    assertNull(System.getProperty("multivaluedConfigPropertyUnset"));
   }
 }