clarified props: more permissive;

--- a/Admin/components/components.sha1	Sat Jul 24 17:06:50 2021 +0200
+++ b/Admin/components/components.sha1	Sat Jul 24 18:01:24 2021 +0200
@@ -132,6 +132,7 @@
 7322d6d84d75c486a58ed36630431db4499e3232  isabelle_setup-20210717-2.tar.gz
 14f8508bcae9140815bb23e430e26d2cbc504b81  isabelle_setup-20210717.tar.gz
 ca801d5c380ea896ee32b309ff19ae5f34538963  isabelle_setup-20210718.tar.gz
+ac9739e38e4fbbfce1a71a0987a57b22f83922d3  isabelle_setup-20210724-1.tar.gz
 127a75ae33e97480d352087fcb9b47a632d77169  isabelle_setup-20210724.tar.gz
 0b2206f914336dec4923dd0479d8cee4b904f544  jdk-11+28.tar.gz
 e12574d838ed55ef2845acf1152329572ab0cc56  jdk-11.0.10+9.tar.gz

--- a/Admin/components/main	Sat Jul 24 17:06:50 2021 +0200
+++ b/Admin/components/main	Sat Jul 24 18:01:24 2021 +0200
@@ -8,7 +8,7 @@
 flatlaf-1.2
 idea-icons-20210508
 isabelle_fonts-20210322
-isabelle_setup-20210724
+isabelle_setup-20210724-1
 jdk-15.0.2+7
 jedit-20210724
 jfreechart-1.5.1

--- a/src/Tools/Setup/src/Build.java	Sat Jul 24 17:06:50 2021 +0200
+++ b/src/Tools/Setup/src/Build.java	Sat Jul 24 18:01:24 2021 +0200
@@ -50,6 +50,8 @@
 
     public static String BUILD_PROPS = "build.props";
     public static String COMPONENT_BUILD_PROPS = "etc/build.props";
+
+    public static String TITLE = "title";
     public static String MODULE = "module";
     public static String NO_BUILD = "no_build";
 
@@ -119,12 +121,7 @@
             }
         }
 
-        public String title() {
-            String title = _props.getProperty("title", "");
-            if (title.isEmpty()) { throw new RuntimeException(error_message("Missing title")); }
-            else return title;
-        }
-
+        public String title() { return _props.getProperty(TITLE, ""); }
 
         public String module_name() { return _props.getProperty(MODULE, ""); }
         public String module_result() { return get_bool(NO_BUILD) ? "" : module_name(); }
@@ -487,7 +484,9 @@
                     shasum = _shasum.toString();
                 }
                 if (fresh || !shasum_old.equals(shasum)) {
-                    System.out.print("### Building " + title + " (" + jar_path + ") ...\n");
+                    if (!title.isEmpty()) {
+                        System.out.print("### Building " + title + " (" + jar_path + ") ...\n");
+                    }
 
                     String isabelle_classpath = Environment.getenv("ISABELLE_CLASSPATH");